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7.3.2 OBX - observation/result segment

The OBX segment is used to transmit a single observation or observation fragment. It represents the smallest indivisible unit of a report. Its structure is summarized in Figure 7-5.

Its principal mission is to carry information about observations in report messages. But the OBX can also be part of an observation order (see Section 4.2, "Order Message Definitions"). In this case, the OBX carries clinical information needed by the filler to interpret the observation the filler makes. For example, an OBX is needed to report the inspired oxygen on an order for a blood oxygen to a blood gas lab, or to report the menstrual phase information which should be included on an order for a pap smear to a cytology lab. Appendix 7A includes codes for identifying many of pieces of information needed by observation producing services to properly interpret a test result. OBX is also found in other HL7 messages that need to include patient clinical information.

Figure 7-5. OBX attributes

SEQ

LEN

DT

OPT

RP/#

TBL#

ITEM#

ELEMENT NAME

1

10

SI

O



00569

Set ID - OBX

2

2

ID

C


0125

00570

Value Type

3

590

CE

R



00571

Observation Identifier

4

20

ST

C



00572

Observation Sub-ID

5

65536 [ The length of the observation value field is variable, depending upon value type. See OBX-2-value type .]

*

C

Y [ May repeat for multipart, single answer results with appropriate data types, e.g., CE, TX, and FT data types.]


00573

Observation Value

6

60

CE

O



00574

Units

7

10

ST

O



00575

References Range

8

5

ID

O

Y/5

0078

00576

Abnormal Flags

9

5

NM

O



00577

Probability

10

2

ID

O

Y

0080

00578

Nature of Abnormal Test

11

1

ID

R


0085

00579

Observ Result Status

12

26

TS

O



00580

Date Last Obs Normal Values

13

20

ST

O



00581

User Defined Access Checks

14

26

TS

O



00582

Date/Time of the Observation

15

60

CE

O



00583

Producer's ID

16

80

XCN

O



00584

Responsible Observer

17

60

CE

O

Y


00936

Observation Method

7.3.2.0 OBX field definitions

7.3.2.1 Set ID - observation simple (SI) 00569

Definition: This field contains the sequence number. For compatibility with ASTM.

7.3.2.2 Value type (ID) 00570

Definition: This field contains the format of the observation value in OBX. It must be valued if OBX-11-Observation result status is not valued with an ‘X". If the value is CE then the result must be a coded entry. When the value type is TX or FT then the results are bulk text. The valid values for the value type of an observation are listed in HL7 table 0125 - Value type.

The observation value must be represented according to the format for the data type defined in Chapter 2, Section 2.8, "Data Types." For example, a PN consists of 6 components, separated by component delimiters.

Although NM is a valid type, observations which are usually reported as numbers will sometimes have the string (ST) data type because non-numeric characters are often reported as part of the result, e.g., >300 to indicate the result was off-scale for the instrument. In the example, ">300", ">" is a symbol and the digits are considered a numeric value. However, this usage of the ST type should be discouraged since the SN (structured numeric) data type now accommodates such reporting and, in addition, permits the receiving system to interpret the magnitude.

All HL7 data types are valid, and are included in Table 0125 except CM, CQ, SI, and ID. For a CM definition to have meaning, the specifics about the CM must be included in the field definition. OBX-5-observation value is a general field definition that is influenced by the data type OBX-3, so CMs are undefined in this context. CQ is invalid because units for OBX-5-observation value are always specified explicitly in an OBX segment with OBX-6 units. SI is invalid because it only applied to HL7 message segments, and ID because it requires a constant field definition.

The RP value (reference pointer) must be used if the actual observation value is not sent in OBX but exists somewhere else. For example, if the observation consists of an image (document or medical), the image itself cannot be sent in OBX. The sending system may in that case opt to send a reference pointer. The receiving system can use this reference pointer whenever it needs access to the actual image through other interface standards, e.g., DICOM, or through appropriate data base servers.

Table 0125 - Value type

Value

Description

AD

Address

CE

Coded Entry

CF

Coded Element With Formatted Values

CK

Composite ID With Check Digit

CN

Composite ID And Name

CP

Composite Price

CX

Extended Composite ID With Check Digit

DT

Date

ED

Encapsulated Data

FT

Formatted Text (Display)

MO

Money

NM

Numeric

PN

Person Name

RP

Reference Pointer

SN

Structured Numeric

ST

String Data.

TM

Time

TN

Telephone Number

TS

Time Stamp (Date & Time)

TX

Text Data (Display)

XAD

Extended Address

XCN

Extended Composite Name And Number For Persons

XON

Extended Composite Name And Number For Organizations

XPN

Extended Person Number

XTN

Extended Telecommunications Number

The full definition of these data types is given in Chapter 2, Section 2.8, "Data Types." The structured numeric (SN) data type, new to version 2.3, provides for reporting ranges (e.g., 3-5 or 10-20), titres (e.g., 1:10), and out-of-range indicators (e.g., >50) in a structured and computer interpretable way.

We allow the FT data type in the OBX segment but its use is discouraged. Formatted text usually implies a meaningful structure e.g., a list of three independent diagnoses reported on different lines. But ideally, the structure in three independent diagnostic statements would be reported as three separate OBX segments.

TX should not be used except to send large amounts of text. In the TX data type, the repeat delimiter can only be used to identify paragraph breaks. Use ST to send short, and possibly encodable, text strings.

7.3.2.3 Observation identifier (CE) 00571

Components: <identifier (ST)> ^ <text (ST)> ^ <name of coding system (ST)> ^ <alternate identifier (ST)> ^ <alternate text (ST)> ^ <name of alternate coding system (ST)>

Definition: This field contains a unique identifier for the observation. The format is that of the Coded Element (CE). Example: 93000.3^P-R interval^A34.

In most systems the identifier will point to a master observation table that will provide other attributes of the observation that may be used by the receiving system to process the observations it receives. A set of message segments for transmitting such master observation tables is described in Chapter 8. The relation of an observation ID to a master observation table is analogous to the relationship between a charge code (in a billing record) and the charge master.

When local codes are used as the first identifier in this field we strongly encourage sending a universal identifier as well to permit receivers to equivalence results from different providers of the same service (e.g., a hospital lab and commercial lab that provides serum potassium to a nursing home). One possible universal identifier is LOINC codes for laboratory and clinical measurements (see Figure 7-3 and the HL7 www listserver); see Section 7.15, "WAVEFORM RESULT DATA TYPES," and Appendix X2 of ASTM E1467 for neurophysiology tests.

7.3.2.4 Observation sub-ID (ST) 00572

Definition: This field is used to distinguish between multiple OBX segments with the same observation ID organized under one OBR. For example, a chest xray report might include three separate diagnostic impressions. The standard requires three OBX segments, one for each impression. By putting a 1 in the Sub-ID of the first of these OBX segments, 2 in the second, and 3 in the third, we can uniquely identify each OBX segment for editing or replacement.

The sub-identifier is also used to group related components in reports such as surgical pathology. It is traditional for surgical pathology reports to include all the tissues taken from one surgical procedure in one report. Consider, for example, a single surgical pathology report that describes the examination of gallbladder and appendix tissue. This report would be transmitted roughly as shown in Figure 7-6.

Figure 7-6. Example of sub-identifier usage

OBR|1|||88304&SURG PATH REPORT...
OBX|1|CE|88304&ANT|1|T57000^GALLBLADDER^SNM...
OBX|2|TX|88304&GDT|1|THIS IS A NORMAL GALLBLADDER...
OBX|3|TX|88304&MDT|1|MICROSCOPIC EXAM SHOWS HISTOLOGICALLY 
 NORMAL GALLBLADDER TISSUE...
OBX|4|CE|88304&IMP|1|M-00100^NML^SNM...
OBX|5|CE|88304&ANT|2|T66000^APPENDIX^SNM...
OBX|6|TX|88304&GDT|2|THIS IS A RED, INFLAMED, SWOLLEN, BOGGY APPENDIX...
OBX|7|TX|88304&MDT|2|INFILTRATION WITH MANY PMN's - INDICATING INFLAMATORY CHANGE...
OBX|8|CE|88304&IMP|2|M-40000^INFLAMMATION NOS^SNM...

The example in Figure 7-6 has two segments for each component of the report, one for each of the two tissues. Thus, there are two 88304&ANT segments; there are two 88304&GDT segments, and there are two 88304&MDT segments. Segments that apply to the gallbladder all have the sub-identifier 1. Segments that apply to the appendix all have sub-identifier 2.

The observation sub ID has other grouping uses. It can be used to organize the reporting of some kinds of fluid intakes and outputs. For example, when intake occurs through multiple intravenous lines; a number of separate observations (OBX segments), the intake volume, the type of intake (Blood, D5W, Plasma, etc.), the site of the IV line, etc. may be needed for each intravenous line, each requiring a separate OBX segment. If more than one IV line is running, we can logically link all of the OBX segments that pertain to the first IV line by assigning them an observation sub ID of 1. We can do the same with the second IV line by assigning them a sub ID 2 and so on. The same would apply to the outputs of surgical drains when there are multiple such drains.

The use of the sub ID to distinguish repeating OBXs for the same observation ID is really a special case of using the sub ID to group, as can be seen if we picture the OBX segments in Figure 7-6 as part of a table where the rows correspond to a particular species of observation and the cells correspond to the sub ID numbers that would be associated with each corresponding OBX.

Distinct Observations

88304&ANT

88304&GDT

80304&MDT

80304&IMP

Sub ID 1st Group

1

1

1

1

Sub ID 2nd Group

2

2

2

2

The use of Sub IDs to group results is equivalent to defining a table, and the use of sub IDs to distinguish repeats is just a special case, represented by one column in this table.

However, this approach introduces ambiguities if we have a set of repeating observations within a group, e.g., if the appendix observations include two impressions as in the 8th and 9th OBXs shown in Figure 7-7. This really represents the existence of a row nested within a single cell of the table given above.

Figure 7-7. Example of sub-identifier usage

OBX|1|CE|880304&ANT|1|T57000^GALLBLADDER^SNM...
OBX|2|TX|880304&GDT|1|THIS IS A NORMAL GALL BLADDER...
OBX|3|TX|880304&MDT|1|MICROSCOPIC EXAMINATION SHOWS HISTOLOGICALLY 
 NORMAL GALLBLADDER TISSUE...
OBX|4|CE|880304&IMP|1|M-00100^NML^SNM...
OBX|5|CE|880304&ANT|2|T57000^APPENDIX^SNM...
OBX|6|TX|880304&GDT|2|THIS IS A RED, INFLAMED APPENDIX...
OBX|7|TX|880304&MDT|2|INFLAMMATION WITH MANY PUS CELLS-ACUTE INFLAMMATION...
OBX|8|CE|880304&IMP|2|M-40000^INFLAMMATION NOS^SNM...
OBX|9|CE|880304&IMP|2|M-30280^FECALITH^SNM...

The text under OBX-5 provides guidance about dealing with two OBXs with the same observation ID and observation sub IDs. They are sent and replaced as a unit. However, some systems will take this to mean that the set of OBXs are to be combined into one composite observation in the receiving system. We suggest the use of a dot and a string (similar to the Dewey Decimal system) when users wish to distinguish each of the repeats within one type, or results within a cell for editing and correction purposes. Using this system, Figure 7-7 would become 7-8. If there are cases where such nesting occurs at even deeper levels, this approach could be extended.

Figure 7-8. Example of sub-identifier usage

OBX|1|CE|880304&ANT|1|T57000^GALLBLADDER^SNM...
OBX|2|TX|880304&GDT|1|THIS IS A NORMAL GALL BLADDER...
OBX|3|TX|880304&MDT|1|MICROSCOPIC EXAMINATION SHOWS HISTOLOGICALLY 
 NORMAL GALLBLADDER TISSUE...
OBX|4|CE|880304&IMP|1|M-00100^NML^SNM...
OBX|5|CE|880304&ANT|2|T57000^APPENDIX^SNM...
OBX|6|TX|880304&GDT|2|THIS IS A RED, INFLAMED APPENDIX...
OBX|7|TX|880304&MDT|2|INFLAMMATION WITH MANY PUS CELLS-ACUTE INFLAMMATION...
OBX|8|CE|880304&IMP|2.1|M-40000^INFLAMMATION NOS^SNM...
OBX|9|CE|880304&IMP|2.2|M-30280^FECALITH^SNM...

Use a null or 1 when there is no need for multiples.

If the observation includes a number of OBXs with the same value for the observation ID OBX-3, then one must use different values for the sub-ID. This is in fact the case of the repeats depicted in Figure 7-8, but without any need to group sets of OBXs. Three such OBXs could be distinguished by using sub-Ids 1,2,e; alternatively, sub-Ids 1.1, 1.2, 1.3 could be used, as shown in Figure 7-8. Figure 7-9 shows and example of an electrocardiograph chest radiograph report with three diagnostic impressions, using 1,2,3 in the sub-ID field to distinguish the three separate results.

Figure 7-9 Example of Sub-ID used to distinguish three independent results with the same observation ID

OBX|1|CE|8601-7^EKG IMPRESSION ^LN|1|^atrial fibrillation|. . .
OBX|2|CE|8601-7^EKG IMPRESSION ^LN|2|^OLD SEPTAL MYOCARDIAL INFARCT| . . .
OBX|3|CE|8601-7^EKG IMPRESSION ^LN|3|^poor R wave progression|. . .

7.3.2.5 Observation value (*) 00573

Definition: This field contains the value observed by the observation producer. OBX-2-value type contains the data type for this field according to which observation value is formatted. It is not a required field because some systems will report only the normalcy/abnormalcy (OBX-8), especially in product experience reporting.

Representation

This field contains the value of OBX-3-observation identifier of the same segment. Depending upon the observation, the data type may be a number (e.g., a respiratory rate), a coded answer (e.g., a pathology impression recorded as SNOMED), or a date-time (the date-time that a unit of blood is sent to the ward). An observation value is always represented as the data type specified in OBX-2-value type of the same segment. Whether numeric or short text, the answer shall be recorded in ASCII text.

Reporting logically independent observations

The main sections of dictated reports, such as radiologic studies or history and physicals, are reported as separate OBX segments. In addition, each logically independent observation should be reported in a separate OBX segment, i.e. one OBX segment should not contain the result of more than one logically independent observation. This requirement is included to assure that the contents of OBX-6-units, OBX-8-abnormal flags, and OBX-9-probability can be interpreted unambiguously. The electrolytes and vital signs batteries, for example, would each be reported as four separate OBX segments. Two diagnostic impressions, e.g., congestive heart failure and pneumonia, would also be reported as two separate OBX segments whether reported as part of a discharge summary or chest xray report. Similarly, two bacterial organisms isolated in a single bacterial culture would be reported as two separate OBX segments.

Though two independent diagnostic statements cannot be reported in one OBX segment, multiple categorical responses are allowed (usually as CE data types separated by repeat delimiters), so long as they are fragments (modifiers) that together construct one diagnostic statement. Right upper lobe (recorded as one code) and pneumonia (recorded as another code), for example, could be both reported in one OBX segment. Such multiple "values" would be separated by repeat delimiters.

Multiple OBX segments with the same observation ID and Sub ID

In some systems, a single observation may include fragments of more than one data type. The most common example is a numeric result followed by coded comments (CE). In this case, the logical observation can be sent in more than one OBX segment. For example, one segment of numeric or string data type for the numeric result and another segment of CE data type for coded comments. If the producer was reporting multiple coded comments they would all be sent in one OBX segment separated by repeat delimiters because they all modified a single logical observation. Multiple OBX segments with the same observation ID and sub ID should always be sent in sequence with the most significant OBX segment (the one that has the normal flag/units and or reference range and status flag) first. The value of OBX-6 through 12 should be null in any following OBX segments with the same OBX-3-observation identifier and OBX-4-observation sub-ID. For the purpose of replacement or deletion, multiple OBX segments with the same observation ID and sub ID are treated as a unit. If any are replaced or deleted, they all are replaced.

Coded values

When an OBX segment contains values of CE data types, the observations are stored as a combination of codes and/or text. In Section 7.4.4, "Example of narrative report messages," examples of results that are represented as CE data types are shown in the first and second OBX segments of OBR 1 and the first and second OBX segments of OBR 2. The observation may be an observation battery ID (for recommended studies), a diagnostic code or finding (for a diagnostic impression), or an anatomic site for a pathology report, or any of the other kinds of coded results.

It is not necessary to always encode the information stored within a coded observation. For example, a chest xray impression could be transmitted as pure text even though it has a CE data type. In this case, the test must be recorded as the second component of the result code, e.g.,

OBX|1|CE|71020&IMP|1|^CONGESTIVE HEART FAILURE.

However, separate impressions, recommendations, etc., even if recorded as pure text, should be recorded in separate result segments. That is, congestive heart failure and pneumonia should not be sent as:

OBX|1|CE|71020&IMP|1|^CONGESTIVE HEART FAILURE AND PNEUMONIA|

but as:

OBX|1|CE|71020&IMP|1|^CONGESTIVE HEART FAILURE| 
OBX|2|CE|71020&IMP|2|^PNEUMONIA|.  

Even better would be fully-coded results that include computer understandable codes (component 1) instead of, or in addition to, the text description (component 2). One may include multiple values in a CE value and these can be mixtures of code and text, but only when they are needed to construct one diagnosis, impression, or concept. When text follows codes as an independent value it would be taken as a modifier or addenda to the codes. E.g.,

OBX|1|CE|710120&IMP^CXR|1|428.0^CONGESTIVE HEART FAILURE^I9C~^MASSIVE HEART

The text in component 2 should be an accurate description of the code in component 1. Likewise, if used, the text in component 5 should be an accurate description of the code in component 4.

7.3.2.6 Units (CE) 00574

Components: <identifier (ST)> ^ <text (ST)> ^ <name of coding system (ST)> ^ <alternate identifier (ST)> ^ <alternate text (ST)> ^ <name of alternate coding system (ST)>

Definition: This field contains the units have a data type of CE. The default coding system for the units codes consists of the ISO+ abbreviation for a single case unit (ISO 2955-83) plus extensions, that do not collide with ISO abbreviations (see introductory section to this chapter). We designate this coding system as ISO+. Both the ISO unit’s abbreviations and the extensions are defined in Section 7.3.2.6.1.2, "ISO and ANSI customary units abbreviations,"and listed in Figure 7-13. The ISO+ abbreviations are the codes for the default coding system. Consequently, when ISO+ units are being used, only ISO+ abbreviations need be sent, and the contents of the units field will be backward compatible to HL7 Version. 2.1.

7.3.2.6.1 Identifying reporting units
7.3.2.6.1.1 Background

When an observation’s value is measured on a continuous scale, one must report the measurement units within the units field of the OBX segment. Since in HL7 version 2.2 of the specification, all fields that report units are of data type CE. The default coding system for the units codes consists of the ISO abbreviation for a single case unit (ISO 2955-83) plus extensions that do not collide with ISO abbreviations. We designate this coding system as ISO+ (see Figure 7-13). Both the ISO unit’s abbreviations and the extensions are defined in Section 7.3.2.6.1.2, "ISO and ANSI customary units abbreviations." The ISO+ abbreviations are the codes for the default coding system. Consequently, when ISO+ units are being used, only ISO+ abbreviations need be sent, and the contents of the units field will be backward compatible to HL7 version 2.1 and ASTM 1238-88.

We strongly encourage observation producers to use ISO+ abbreviated units exclusively, but permit the use of other code systems, including US customary units (ANSI X3.50) and locally defined codes where necessary. Local units are designated L or 99zzz where z is an alpha numeric character (see figures 7-2 and 73). ANSI X3.50 -1986 provides an excellent description of these standards, as well as a table of single case abbreviations for US customary units such as foot or gallon.

We had originally intended to include the ANSI X3.50 - 1986 US customary units in the default ISO+ coding system. However, there are overlaps between ISO’s abbreviations and the abbreviations for US customary units. For example, ft is the abbreviation for foot in US customary units and for femtotesla in ISO; pt is the abbreviation for pint in US customary and for picotesla in ISO. (Be aware that the ANSI document also differs from the ISO document regarding the abbreviation of a few ISO units, as well.) In order to avoid potential ambiguity, we have defined another coding system, designated ANS+. It includes the US customary units (e.g., feet, pounds) and ISO abbreviations defined in ANSI X3.50-1986, as well as other non-metric units listed in Figure 7-13 and the ISO combinations of these units. Be aware that a few of the ANSI ISO unit abbreviations differ from their abbreviations in ISO (see note at bottom of Figure 7-13).

Because the ANS+ specification includes both ISO and US customary units, as well as miscellaneous non-metric units, some of the abbreviations are ambiguous. Although there should be little confusion, in the context of a particular observation, this ambiguity is a good reason for avoiding ANS+ unit codes when possible.

When ANS+ units codes (abbreviations) are being transmitted, ANS+ must be included in the 3rd (6th) component of the field. If the units of distance were transmitted as meters (ISO+) it would be transmitted as m because ISO+ is the default coding system for units. However, if transmitted in the US customary units of feet, the units would be transmitted as ft^^ANS+. When required, the full text of the units can be sent as the second component in keeping with the CE data type conventions.

Both ISO and ANSI also provide a set of mixed case abbreviations, but these abbreviations cannot be translated to single case without loss of meaning, and should not be used in this specification whose content is required to be case insensitive.

7.3.2.6.1.2 ISO and ANSI customary units abbreviations

ISO builds its units from seven base dimensions measured as meters, kilograms, seconds, amperes, kelvins, moles and candelas (see Figure 7-10). Other units can be derived from these by adding a prefix to change the scale and/or by creating an algebraic combination of two or more base or derived units. However, some derived units have acquired their own abbreviations (see Figure 7-10). Abbreviations for U.S. customary units are given in Figure 7-11.

The ISO rules, well explained in ANSI X3.50, provide a way to create units of different scales by adding multiplier prefixes. These prefixes can be expressed as words or abbreviations. In this standard we are only concerned with the abbreviations.

Figure 7-10. ISO single case units abbreviations

Units

Abbreviation

Units

Abbreviation

Units

Abbreviation

Base units code/abbreviations

ampere

a

kelvin

k

meter

m

candela

cd

kilogram

kg

mole

mol





second

s

Derived units with specified name and abbreviation

coulomb

c

hour

hr

pascal

pal

day

d

joule

j

volt

v

degree Celsius

cel

minute (ti)

min

watt

w

farad

f

newton

n

weber

wb

hertz

hz

ohm

ohm

year

ann

Other units

atomic mass unit

u

grey

gy

minute of arc

mnt

bel

b

henry

h

radian

rad

decibel

db

liter

l

siemens

sie

degree

deg

lumen

lm

steradian

sr

gram

g

lux

lx

tesla

t

See ISA 2955-1983 for full set

The ISO abbreviations for multiplier prefixes are given in Figure 7-12. Prefixes ranging from 10-24 (1/billion billionth) to 1024 (a billion billion) are available. The single case abbreviation for kilo (x1000) is k. A unit consisting of 1000 seconds would be abbreviated as ks, 1000 grams as kg, 1000 meters as km, and so on. Some prefixes share the abbreviation of a base unit. Farad and femto, for example, (10-18) both have the abbreviation of f. To avoid confusion, ISO forbids the use of solitary prefixes. It also deprecates the use of two prefixes in one complex unit. Thus, f always means farad, ff would mean 1 million billionth of a farad. Compound prefixes are not allowed.

A unit can be raised to an exponential power. Positive exponents are represented by a number immediately following a unit’s abbreviation, i.e., a square meter would be denoted by m2. Negative exponents are signified by a negative number following the base unit, e.g., 1/m2 would be represented as m-2 Fractional exponents are expressed by a numeric fraction in parentheses: the square root of a meter would be expressed as m(1/2). The multiplication of units is signified by a period (.) between the units, e.g., meters X seconds would be denoted m.s. Notice that spaces are not permitted. Division is signified by a slash (/) between two units, e.g. meters per second would be denoted as m/s. Algebraic combinations of ISO unit abbreviations constructed by dividing, multiplying, or exponentiating base ISO units, are also valid ISO abbreviations units. Exponentiation has precedence over multiplication or division. For example, microvolts squared per hertz (a unit of spectral power) would be denoted uv2/hz and evaluated as uv 2/hz while microvolts per square root of hertz (a unit of spectral amplitude) would be denoted uv/hz(1/2) and evaluated as uv/hz½ . If more than one division operator is included in the expression the associations should be parenthesized to avoid any ambiguity, but the best approach is to convert a/(b/c) to a.c/b or a.c.b-1 to simplify the expression.

Figure 7-11. ANSI+ unit codes for some U.S. customary units

Units

Abbreviation

Units

Abbreviation

Units

Abbreviation

LENGTH

VOLUME

TIME

inch

in

cubic foot

cft

year

yr

foot

ft

cubic inch

cin

month

mo

mile (statute)

mi

cubic yard

cyd

week

wk

mautical mile

nmi

tablespoon

tbs

day

d

rod

rod

teaspoon

tsp

hour

hr

yard

yd

pint

pt

minute

min



quart

qt

second

sec



gallon

gal





ounce (fluid)

foz



AREA

MASS



square foot

sqf

dram

dr



square inch

sin

grain

gr (avoir)



square yard

syd

ounce (weight)

oz





pound

lb



Other ANSI units, derived units, and miscellanous

**British thermal unit

btu

**degrees fahrenheit

degf

**millirad

mrad

cubic feet/minute

cft/min

**feet/minute

ft/min

**RAD

rad

Note: the abbreviations for conventional U.S. units of time are the same as ISO, except for year. ISO = ANN, AMSI = yr. The metric units in X3.50 are the same as ISO, except for: pascal ("pa" in ANSI, "pal" in ISO); ANSI uses "min" for both time and arc while ISO uses "mnt" for minutes of arc; and in ISA seconds are abbreviated "s", in ANSI, "sec".

This list is not exhaustive. Refer to ANSI X3.50-1986, Table 1, for other metric and standard U.S. units.

**Non-metric units not explicitly listed in ANSI

Figure 7-12. Single case ISO abbreviations for multiplier prefixes

Prefix


Code

Prefix


Code

yotta*

1024

ya

yocto

10-24

y

zetta*

1021

za

zepto

10-21

z

exa

1018

ex

atto

10-18

a

peta

1015

pe

femto

10-15

f

tera

1012

t

pico

10-12

p

giga

109

g

nano

10-9

n

mega

106

ma

micro

10-6

u

kilo

103

k

milli

10-3

m

hecto

102

h

centi

10-2

c

deca

101

da

deci

10-1

d

*These abbreviations are not defined in the ISO specification for single case abbreviations.

Figure 7-13 lists the abbreviations for common ISO derived units. It also includes standard unit abbreviations for common units, e.g., Milliequivalents, and international units, mm(Hg), and for counting per which we denote by a division sign, a denominator, but no numerator, e.g., /c, that are not part of the above referenced ISO standards. We have extended the units table to better accommodate drug routes and physiologic measures, and otherwise fill in gaps in Version 2.2.

We have generally followed the IUPAC 1995 Silver Book2 in the definitions of units. However, IUPAC specifies standards for reporting or displaying units and employs 8-bit data sets to distinguish them. This standard is concerned with the transmission of patient information. Therefore, we have restricted ourselves to case insensitive alphabetic characters and a few special characters (e.g., ".", "/", "( ", ") ","*", and "_" ) to avoid any possible confusion in the transmission. Therefore, we use ISO 2955-1983 (Information processing -- representation of SI and other units in systems with limited character sets) and ANSI X3.50-1986 (Representations for U.S. customary, SI, and other units to be used in systems with limited character sets) case insensitive units abbreviations where they are defined. This means that in some cases, IUPAC abbreviations have different abbreviations in ISO+ even when the IUPAC abbreviations use only standard alphabetic characters. For example, Pascal is abbreviated Pa in IUPAC but PAL in ISO+ (following ISO 2955) because Pa in a case insensitive context also means Picoampere. However, the requirements for transmission do not preclude usage of IUPAC standards for presentation on paper or video display reports to end users.

All unit abbreviations are case insensitive. One could write milliliters as ML, ml, or mL. In this table we have used lower case for all of the abbreviations except for the letter L which we represent in upper case so that readers will not confuse it with the numeral one (1). This is just a change in presentation, not a change in the standard. Systems should continue to send the codes as upper or lower case as they always have.

Figure 7-13. Common ISO derived units and *ISO extensions

Code/Abbr.

Name

/(arb_u)

*1 / arbitrary unit

/iu

*1 / international unit

/kg

*1 / kilogram

/L

1 / liter

1/mL

*1 / milliliter

10.L/min

*10 x liter / minute

10.L /(min.m2)

*10 x (liter / minute) / meter2 = liter / (minute ´ meter2)

10*3/mm3

*103 / cubic millimeter (e.g., white blood cell count)

10*3/L

*103 / Liter

10*3/mL

*103 / milliliter

10*6/mm3

*106 / millimeter3

10*6/L

*106 / Liter

10*6/mL

*106 / milliliter

10*9/mm3

*109 / millimeter3

10*9/L

*109 / Liter

10*9/mL

*109 / milliliter

10*12/L

*1012 / Liter

10*3(rbc)

*1000 red blood cells

a/m

Ampere per meter

(arb_u)

*Arbitrary unit

bar

Bar (pressure; 1 bar = 100 kilopascals)

/min

Beats Per Minute

bq

Becquerel

(bdsk_u)

*Bodansky Units

(bsa)

*Body surface area

(cal)

*Calorie

1

*Catalytic Fraction

/L

Cells / Liter

cm

Centimeter

cm_h20

* Centimeters of water =H20 (pressure)

cm_h20.s/L

Centimeters H20 / (liter / second) = (centimeters H20 ´ second) / liter (e.g., mean pulmonary resistance)

cm_h20/(s.m)

(Centimeters H20 / second) / meter = centimeters H20 / (second ´ meter) (e.g., pulmonary pressure time product)

(cfu)

*Colony Forming Units

m3/s

Cubic meter per second

d

Day

db

Decibels

dba

*Decibels a Scale

cel

Degrees Celsius

deg

Degrees of Angle

(drop)

Drop

10.un.s/cm5

Dyne ´ Second / centimeter5 (1 dyne = 10 micronewton = 10 un) (e.g., systemic vascular resistance)

10.un.s/(cm5.m2)

((Dyne ´ second) / centimeter5) / meter2 = (Dyne ´ second) / (centimeter5 ´ meter2) (1 dyne = 10 micronewton = 10 un) (e.g., systemic vascular resistance/body surface area)

ev

Electron volts (1 electron volt = 160.217 zeptojoules)

eq

Equivalent

f

Farad (capacitance)

fg

Femtogram

fL

Femtoliter

fmol

Femtomole

/mL

*Fibers / milliliter

g

Gram

g/d

*Gram / Day

g/dL

Gram / Deciliter

g/hr

Gram / Hour

g/(8.hr)

*Gram / 8 Hour Shift

g/kg

Gram / Kilogram (e.g., mass dose of medication per body weight)

g/(kg.d)

(Gram / Kilogram) / Day = gram / (kilogram ´ day) (e.g., mass dose of medication per body weight per day)

g/(kg.hr)

(Gram / Kilogram) / Hour = gram / (kilogram ´ hour) (e.g., mass dose of medication per body weight per hour)

g/(8.kg.hr)

(Gram / Kilogram) /8 Hour Shift = gram / (kilogram ´ 8 hour shift) (e.g., mass dose of medication per body weight per 8 hour shift)

g/(kg.min)

(Gram / Kilogram) / Minute = gram / (kilogram ´ minute) (e.g., mass dose of medication per body weight per minute)

g/L

Gram / Liter

g/m2

Gram / Meter2

(e.g., mass does of medication per body surface area)

g/min

Gram / Minute

g.m/(hb)

Gram ´ meter / heart beat

(e.g., ventricular stroke work)

g.m/((hb).m2)

(Gram ´ meter/ heartbeat) / meter2 = (gram ´ meter) / (heartbeat ´ meter2)

(e.g., ventricular stroke work/body surface area, ventricular stroke work index)

g(creat)

*Gram creatinine

g(hgb)

*Gram hemoglobin

g.m

Gram meter

g(tot_nit)

*Gram total nitrogen

g(tot_prot)

*Gram total protein

g(wet_tis)

*Gram wet weight tissue

gy

Grey (absorbed radiation dose)

hL

Hectaliter = 102 liter

h

Henry

in

Inches

in_hg

Inches of Mercury (=Hg)

iu

*International Unit

iu/d

*International Unit / Day

iu/hr

*International Unit / Hour

iu/kg

International Unit / Kilogram

iu/L

*International Unit / Liter

iu/mL

*International Unit / Milliliter

iu/min

*International Unit / Minute

j/L

Joule/liter

(e.g., work of breathing)

kat

*Katal

kat/kg

*Katal / Kilogram

kat/L

*Katal / Liter

k/watt

Kelvin per watt

(kcal)

Kilocalorie (1 kcal = 6.693 kilojoule)

(kcal)/d

*Kilocalorie / Day

(kcal)/hr

*Kilocalorie / Hour

(kcal)/(8.hr)

*Kilocalorie / 8 Hours Shift

kg

Kilogram

kg(body_wt)

* kilogram body weight

kg/m3

Kilogram per cubic meter

kh/h

Kilogram per hour

kg/L

Kilogram / liter

kg/min

Kilogram per minute

kg/mol

Kilogram / mole

kg/s

Kilogram / second

kg/(s.m2)

(Kilogram / second)/ meter2 = kilogram / (second ´ meter2)

kg/ms

Kilogram per square meter

kg.m/s

Kilogram meter per second

kpa

Kilopascal (1 mmHg = 0.1333 kilopascals)

ks

Kilosecond

(ka_u)

King-Armstrong Unit

(knk_u)

*Kunkel Units

L

Liter

L/d

*Liter / Day

L/hr

Liter / hour

L/(8.hr)

*Liter / 8 hour shift

L/kg

Liter / kilogram

L/min

Liter / minute

L/(min.m2)

(Liter / minute) / meter2 = liter / (minute ´ meter2)

(e.g., cardiac output/body surface area = cardiac index)

L/s

Liter / second

(e.g., peak expiratory flow)

L.s

Liter / second / second2 = liter ´ second

lm

Lumen

lm/m2

Lumen / Meter2

(mclg_u)

*MacLagan Units

mas

Megasecond

m

Meter

m2

Meter2

(e.g., body surface area)

m/s

Meter / Second

m/s2

Meter / Second2

ueq

*Microequivalents

ug

Microgram

ug/d

Microgram / Day

ug/dL

Microgram / Deciliter

ug/g

Microgram / Gram

ug/hr

*Microgram / Hour

ug(8hr)

Microgram / 8 Hour Shift

ug/kg

Microgram / Kilogram

mg/(kg.d)

(Microgram / Kilogram) /Day = microgram / (kilogram ´ day) (e.g., mass dose of medication per patient body weight per day)

mg/(kg.hr)

(Microgram / Kilogram) / Hour = microgram / (kilogram ´ hours) (e.g., mass dose of medication per patient body weight per hour)

mg/(8.hr.kg)

(Microgram / Kilogram) / 8 hour shift = microgram / (kilogram ´ 8 hour shift)

(e.g., mass dose of medication per patient body weight per 8 hour shift)

mg/(kg.min)

(Microgram / Kilogram) / Minute = microgram / (kilogram ´ minute)

(e.g., mass dose of medication per patient body weight per minute)

ug/L

Microgram / Liter

ug/m2

Microgram / Meter2 (e.g., mass dose of medication per patient body surface area)

ug/min

Microgram / Minute

uiu

*Micro international unit

ukat

*Microkatel

um

Micrometer (Micron)

umol

Micromole

umol/d

Micromole / Day

umol/L

Micromole / Liter

umol/min

Micromole / Minute

us

Microsecond

uv

Microvolt

mbar

Millibar (1 millibar = 100 pascals)

mbar.s/L

Millibar / (liter / second) =(millibar ´ second) / liter (e.g., expiratory resistance)

meq

*Milliequivalent

meq/d

*Milliequivalent / Day

meq/hr

*Milliequivalent / Hour

meq/(8.hr)

Milliequivalent / 8 Hour Shift

meq/kg

Milliequivalent / Kilogram (e.g., dose of medication in milliequivalents per patient body weight)

meq/(kg.d)

(Milliequivalents / Kilogram) / Day = milliequivalents / (kilogram ´ day) (e.g., dose of medication in milliequivalents per patient body weight per day)

meq/(kg.hr)

(Milliequivalents / Kilogram) / Hour = milliequivalents / (kilogram ´ hour) (e.g., dose of medication in milliequivalents per patient body weight per hour)

meq/(8.hr.kg)

(Milliequivalents / Kilogram) / 8 Hour Shift = milliequivalents / (kilogram ´ 8 hour shift) (e.g., dose of medication in milliequivalents per patient body weight per 8 hour shift)

meq/(kg.min)

(Milliequivalents / Kilogram) / Minute = milliequivalents / (kilogram ´ minute) (e.g., dose of medication in milliequivalents per patient body weight per minute)

meq/L

Milliequivalent / Liter


Milliequivalent / Meter2 (e.g., dose of medication in milliequivalents per patient body surface area)

meq/min

Milliequivalent / Minute

mg

Milligram

mg/m3

Milligram / Meter3

mg/d

Milligram / Day

mg/dL

Milligram / Deciliter

mg/hr

Milligram / Hour

mg/(8.hr)

Milligram / 8 Hour shift

mg/kg

Milligram / Kilogram

mg/(kg.d)

(Milligram / Kilogram) / Day = milligram / (kilogram ´ day) (e.g., mass dose of medication per patient body weight per day)

mg/(kg.hr)

(Milligram / Kilogram) / Hour = milligram/ (kilogram ´ hour) (e.g., mass dose of medication per patient body weight per hour)

mg/(8.hr.kg)

(Milligram / Kilogram) /8 Hour Shift = milligram / (kilogram ´ 8 hour shift) (e.g., mass dose of medication per patient body weight per 8 hour shift)

mg/(kg.min)

(Milligram / Kilogram) / Minute = milligram / (kilogram ´ minute) (e.g., mass dose of medication per patient body weight per hour)

mg/L

Milligram / Liter

mg/m2

Milligram / Meter2 (e.g., mass dose of medication per patient body surface area)

mg/min

Milligram / Minute

mL

Milliliter

mL/cm_h20

Milliliter / Centimeters of Water (H20) (e.g., dynamic lung compliance)

mL/d

*Milliliter / Day

mL/(hb)

Milliliter / Heart Beat (e.g., stroke volume)

mL/((hb).m2)

(Milliliter / Heart Beat) / Meter2 = Milliliter / (Heart Beat ´ Meter2) (e.g., ventricular stroke volume index)

mL/hr

*Milliliter / Hour

mL/(8.hr)

*Milliliter / 8 Hour Shift

mL/kg

Milliliter / Kilogram (e.g., volume dose of medication or treatment per patient body weight)

mL/(kg.d)

(Milliliter / Kilogram) / Day = milliliter / (kilogram ´ day) (e.g., volume dose of medication or treatment per patient body weight per day)

mL/(kg.hr)

(Milliliter / Kilogram) / Hour = milliliter / (kilogram ´ hour) (e.g., volume dose of medication or treatment per patient body weight per hour)

mL/(8.hr.kg)

(Milliliter / Kilogram) / 8 Hour Shift = milliliter / (kilogram ´ 8 hour shift) (e.g., volume dose of medication or treatment per body weight per 8 hour shift)

mL/(kg.min)

(Milliliter / Kilogram) / Minute = milliliter / (kilogram ´ minute) (e.g., volume dose of medication or treatment per patient body weight per minute)

mL/m2

Milliliter / Meter2 (e.g., volume of medication or other treatment per patient body surface area)

mL/mbar

Milliliter / Millibar (e.g., dynamic lung compliance)

mL/min

Milliliter / Minute

mL/(min.m2)

(Milliliter / Minute) / Meter2 = milliliter / (minute ´ meter2) (e.g., milliliters of prescribed infusion per body surface area; oxygen consumption index)

mL/s

Milliliter / Second

mm

Millimeter

mm(hg)

*Millimeter (HG) (1 mm Hg = 133.322 kilopascals)

mm/hr

Millimeter/ Hour

mmol/kg

Millimole / Kilogram (e.g., molar dose of medication per patient body weight)

mmol/(kg.d)

(Millimole / Kilogram) / Day = millimole / (kilogram ´ day) (e.g., molar dose of medication per patient body weight per day)

mmol/(kg.hr)

(Millimole / Kilogram) / Hour = millimole / (kilogram ´ hour) (e.g., molar dose of medication per patient body weight per hour)

mmol/(8.hr.kg)

(Millimole / Kilogram) / 8 Hour Shift = millimole / (kilogram ´ 8 hour shift) (e.g., molar dose of medication per patient body weight per 8 hour shift)

mmol/(kg.min)

(Millimole / Kilogram) / Minute = millimole / (kilogram ´ minute) (e.g., molar dose of medication per patient body weight per minute)

mmol/L

Millimole / Liter

mmol/hr

Millimole / Hour

mmol/(8hr)

Millimole / 8 Hour Shift

mmol/min

Millimole / Minute

mmol/m2

Millimole / Meter2 (e.g., molar dose of medication per patient body surface area)

mosm/L

*Milliosmole / Liter

ms

Milliseconds

mv

Millivolts

miu/mL

*Milliunit / Milliliter

mol/m3

Mole per cubic meter

mol/kg

Mole / Kilogram

mol/(kg.s)

(Mole / Kilogram) / Second = mole / (kilogram ´ second)

mol/L

Mole / Liter

mol/s

Mole / Second

ng

Nanogram

ng/d

Nanogram / Day

ng/hr

*Nanogram / Hour

ng/(8.hr)

Nanogram / 8 Hour shift

ng/L

Nanogram / Liter

ng/kg

Nanogram / Kilogram (e.g., mass dose of medication per patient body weight)

ng/(kg.d)

(Nanogram / Kilogram) / Day = nanogram / (kilogram ´ day) (e.g., mass dose of medication per patient body weight per day)

ng/(kg.hr)

(Nanogram / Kilogram) / Hour = nanogram / (kilogram ´ hour) (e.g., mass dose of medication per patient body weight per hour)

ng/(8.hr.kg)

(Nanogram / Kilogram) / 8 Hour Shift = nanogram / (kilogram ´ 8 hour shift) (e.g., mass dose of medication per patient body weight per 8 hour shift)

ng/(kg.min)

(Nanogram / Kilogram) / Minute = nanogram / (kilogram ´ minute) (e.g., mass dose of medication per patient body weight per minute)

ng/m2

Nanogram / Meter2 (e.g., mass dose of medication per patient body surface area)

ng/mL

Nanogram / Milliliter

ng/min

*Nanogram / Minute

ng/s

*Nanogram / Second

nkat

*Nanokatel

nm

Nanometer

nmol/s

Nanomole / Second

ns

Nanosecond

n

Newton (force)

n.s

Newton second

(od)

*O.D. (optical density)

ohm

Ohm (electrical resistance)

ohm.m

Ohm meter

osmol

Osmole

osmol/kg

Osmole per kilogram

osmol/L

Osmole per liter

/m3

*Particles / Meter3

/L

*Particles / Liter

/(tot)

*Particles / Total Count

(ppb)

*Parts Per Billion

(ppm)

*Parts Per Million

(ppth)

Parts per thousand

(ppt)

Parts per trillion (10^12)

pal

Pascal (pressure)

/(hpf)

*Per High Power Field

(ph)

*pH

pa

Picoampere

pg

Picogram

pg/L

Picogram / Liter

pg/mL

Picogram / Milliliter

pkat

*Picokatel

pm

Picometer

pmol

*Picomole

ps

Picosecond

pt

Picotesla

(pu)

*P.U.

%

Percent

dm2/s2

Rem (roentgen equivalent man) = 10-2 meter2 / second2 = decimeter2 / second2 Dose of ionizing radiation equivalent to 1 rad of x-ray or gamma ray) [From Dorland's Medical Dictionary]

sec

Seconds of arc

sie

Siemens (electrical conductance)

sv

Sievert

m2/s

Square meter / second

cm2/s

Square centimeter / second

t

Tesla (magnetic flux density)

(td_u)

Todd Unit

v

Volt (electric potential difference)

1

Volume Fraction

wb

Weber (magnetic flux)

*Starred items are not genuine ISO, but do not conflict.

†This approach to units is discouraged by IUPAC. We leave them solely for backwards compatibility


7.3.2.6.1.3 Local unit codes

Local codes can be used for the units by indicating the code source of 99zzz in the third component (where 99zzz is an alpha-numeric string). In the case of local codes, the text name of the codes or the description of the units should also be transmitted (in the second component), so that the receiving system can compare the results with results for the same measurement sent by another service (refer to Chapter 2, Section 2.8, "Data Types"). An "L" should be stored in the third component to indicate that the code is locally defined. More specialized local code designations, as specified in the CE data type definition, can also be employed.

7.3.2.7 References range (ST) 00575

Components: for numeric values in the format:

a) lower limit-upper limit (when both lower and upper limits are defined, e.g., for potassium 3.5 - 4.5)

b) > lower limit (if no upper limit, e.g., >10)

c) < upper limit (if no lower limit, e.g., <15)

alphabetical values: the normal value may be reported in this location

Definition: When the observation quantifies the amount of a toxic substance, then the upper limit of the range identifies the toxic limit. If the observation quantifies a drug, the lower limits identify the lower therapeutic bounds and the upper limits represent the upper therapeutic bounds above which toxic side effects are common.

7.3.2.8 Abnormal flags (ID) 00576

Definition: This field contains a table lookup indicating the normalcy status of the result. We strongly recommend sending this value when applicable. If the observation is an antimicrobial susceptibility, the interpretation codes are: S=susceptible; R=resistant; I=intermediate; MS=moderately susceptible; VS=very susceptible. (See ASTM 1238 - review for more details). Refer to HL7 table 0078 - Abnormal flags for valid entries.

When the laboratory can discern the normal status of a textual report, such as chest X-ray reports or microbiologic culture, these should be reported as N when normal and A when abnormal. Multiple codes, e.g., abnormal and worse, would be separated by a repeat delimiter, e.g., A~W.

Table 0078 Abnormal flags

Value

Description

L

Below low normal

H

Above high normal

LL

Below lower panic limits

HH

Above upper panic limits

<

Below absolute low-off instrument scale

>

Above absolute high-off instrument scale

N

Normal (applies to non-numeric results)

A

Abnormal (applies to non-numeric results)

AA

Very abnormal (applies to non-numeric units, analogous to panic limits for numeric units)

null

No range defined, or normal ranges don't apply

U

Significant change up

D

Significant change down

B

Better--use when direction not relevant

W

Worse--use when direction not relevant

For microbiology susceptibilities only:

S

Susceptible

R

Resistant

I

Intermediate

MS

Moderately susceptible

VS

Very susceptible

Results may also be reported in shorthand by reporting the normalcy status without specifying the exact numeric value of the result. Such shorthand is quite common in clinical notes, where physicians will simply say that the glucose result was normal. Such shorthand reporting is also seen in drug experience reporting. In such cases, the result can be reported in the OBX by reporting the normalcy code in OBX-8-abnormal flags without specifying any value in OBX-5-observation value.

7.3.2.9 Probability (NM) 00577

Definition: This field contains the probability of a result being true for results with categorical values. It mainly applies to discrete coded results. It is a decimal number represented as an ASCII string that must be between 0 and 1, inclusive.

7.3.2.10 Nature of abnormal test (ID) 00578

Definition: This field contains the nature of the abnormal test. Refer to HL7 table 0080 - Nature of abnormal testing for valid values. As many of the codes as apply may be included, separated by repeat delimiters. For example, normal values based on age, sex, and race would be codes as A~S~R.

Table 0080 Nature of abnormal testing

Value

Description

A

An age-based population

N

None - generic normal range

R

A race-based population

S

A sex-based population

7.3.2.11 Observ result status (ID) 00579

Definition: This field contains the observation result status. Refer to HL7 table 0085 - Observation result status for valid values. This field reflects the current completion status of the results for one Observation Identifier.

It is a required field. Previous version of HL7 stated this implicitly by defining a default value of "F." Code F indicates that the result has been verified to be correct and final. Code W indicates that the result has been verified to be wrong (incorrect); a replacement (corrected) result may be transmitted later. Code C indicates that data contained in the OBX-5-observation value field are to replace previously transmitted (verified and) final result data with the same observation ID (including suffix, if applicable) and observation sub-ID usually because the previous results were wrong. Code D indicates that data previously transmitted in a result segment with the same observation ID (including suffix) and observation sub-ID should be deleted. When changing or deleting a result, multiple OBX segments with the same observation ID and observation sub-ID are replaced or deleted as a unit. Normal progression of results through intermediate (e.g., ‘gram positive cocci’) to final (e.g., ‘staphylococcus aureus’) should not be transmitted as C (correction); they should be transmitted as P or S (depending upon the specific case) until they are final.

Table 0085 - Observation result status codes interpretation

Value

Description

C

Record coming over is a correction and thus replaces a final result

D

Deletes the OBX record

F

Final results; Can only be changed with a corrected result.

I

Specimen in lab; results pending

P

Preliminary results

R

Results entered -- not verified

S

Partial results

X

Results cannot be obtained for this observation

U

Results status change to Final. without retransmitting results already sent as ‘preliminary.’ E.g., radiology changes status from preliminary to final

W

Post original as wrong, e.g., transmitted for wrong patient

7.3.2.12 Effective date last obs normal value (TS) 00580

Definition: This field contains the changes in the observation methods that would make values obtained from the old method not comparable with those obtained from the new method.

Null if there are no normals or units. If present, a change in this date compared to date-time recorded, the receiving system’s test dictionary should trigger a manual review of the results to determine whether the new observation ID should be assigned a new ID in the local system to distinguish the new results from the old.

7.3.2.13 User defined access checks (ST) 00581

Definition: This field permits the producer to record results-dependent codes for classifying the observation at the receiving system. This field should be needed only rarely, because most classifications are fixed attributes of the observation ID and can be defined in the associated observation master file (see description in Chapter 8).

However, there are a few cases when such controls vary with the value of the observation in a complex way that the receiving system would not want to re-calculate. An example is an antimicrobial susceptibility result. Some systems prefer to display only the susceptibility results of inexpensive antimicrobials depending upon the organism, the source of the specimen and the patients allergy status. The sending service wants to send all of the susceptibilities so that certain privileged users (e.g., Infectious Disease specialists) can review all of the results but nonprivileged users would see only the "preferred" antimicrobials to which the organism was susceptible. We expect that other cases also occur.

7.3.2.14 Date-time of the observation (TS) 00582

Definition: This field is required in two circumstances. The first is when the observations reported beneath one report header (OBR) have different dates. This could occur in the case of queries, timed test sequences, or clearance studies where one measurement within a battery may have a different time than another measurement.

It is also needed in the case of OBX segments that are being sent by the placer to the filler, in which case the date of the observation being transmitted is likely to have no relation to the date of the requested observation. In France, requesting services routinely send a set of the last observations along with the request for a new set of observations. The date of these observations is important to the filler laboratories.

In all cases, the observation date-time is the physiologically relevant date-time or the closest approximation to that date-time. In the case of tests performed on specimens, the relevant date-time is the specimen’s collection date-time. In the case of observations taken directly on the patient (e.g., X-ray images, history and physical), the observation date-time is the date-time that the observation was performed.

7.3.2.15 Producer's ID (CE) 00583

Components: <identifier (ST)> ^ <text (ST)> ^ <name of coding system (ST)> ^ <alternate identifier (ST)> ^ <alternate text (ST)> ^ <name of alternate coding system (ST)>

Definition: This field contains a unique identifier of the responsible producing service. It should be reported explicitly when the test results are produced at outside laboratories, for example. When this field is null, the receiving system assumes that the observations were produced by the sending organization. This information supports CLIA regulations in the US. The code for producer ID is recorded as a CE data type. In the US, the Medicare number of the producing service is suggested as the identifier.

7.3.2.16 Responsible observer (XCN) 00584

Components: <ID number (ST)> ^<family name (ST)> ^ <given name (ST)> ^ <middle initial or name (ST)> ^ <suffix (e.g., JR or III) (ST)> ^ <prefix (e.g., DR) (ST)> ^ <degree (e.g., MD) (ST)> ^ <source table (IS)> ^<assigning authority (HD)> ^<name type (ID)> ^<identifier check digit (ST)> ^ <code identifying the check digit scheme employed (ID)> ^ <identifier type code (IS)> ^ <assigning facility ID (HD)>

Subcomponents of assigning authority: <namespace ID (IS)> & <universal ID (ST)> & <univerwsal ID type (ID)>

Subcomponents of assigning facility ID: <namespace ID (IS)> & <universal ID (ST)> & <univerwsal ID type (ID)>

Definition: When required, this field contains the identifier of the individual directly responsible for the observation (i.e., the person who either performed or verified it). In a nursing service, the observer is usually the professional who performed the observation (e.g., took the blood pressure). In a laboratory, the observer is the technician who performed or verified the analysis. The code for the observer is recorded as a CE data type. If the code is sent as a local code, it should be unique and unambiguous when combined with OBX-15-producer ID.

7.3.2.17 Observation method (CE) 00936

Components: <identifier (ST)> ^ <text (ST)> ^ <name of coding system (ST)> ^ <alternate identifier (ST)> ^ <alternate text (ST)> ^ <name of alternate coding system (ST)>

This optional field can be used to transmit the method or procedure by which an observation was obtained when the sending system wishes to distinguish among one measurement obtained by different methods and the distinction is not implicit in the test ID. Chemistry laboratories do not usually distinguish between two different methods used to measure a given serum constituent (e.g., serum potassium) as part of the test name. See the LOINC Users Manual [ LOINC Committee. Logical Observation Identifier Names and Codes. Indianapolis: Regenstrief Institute and LOINC Committee, 1995. c/o Kathy Hutchins, 1001 West 10th Street RG-5, Indianapolis, IN 46202. 317/630-7433. Available via FTP/Gopher (dumccss.mc.duke.edu/standards/HL7/termcode/loinclab) and World Wide Web (http://dumccss.mc.duke.edu/standards/HL7/termcode/loinc.htm). The LOINC Code System is described in Forrey AW, McDonald CJ, DeMoor G, Huff SM, Leavelle D, Leland D, et.al. Logical Observation Identifier Names and Codes (LOINC) database: a public use set of codes and names for electronic reporting of clinical laboratory test results. Clinical Chemistry 1996;42:81-90] for a more complete discussion of these distinctions. If an observation producing service wanted to report the method used to obtain a particular observation, and the method was NOT embedded in the test name, they can use this field.

The Centers for Disease Control and Prevention (CDC) Method Code (CDCM) (see Figure 7-3) is one candidate code system for reporting methods/instruments. EUCLIDES method codes are another. User-defined tables are an alternative.

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