Components: <namespace ID (IS)> ^ <universal ID (ST)> ^ <universal ID type (ID)>
The HD is designed to be a more powerful application identifier. It is also designed to be used either as a local version of a site defined application identifier or a publically assigned UID. Syntactically, the HD is a group of two application identifiers: one defined by the first component, and one defined by the second and third components.
The HD allows any site to act as an assigning authority (on a local or user-defined basis), even if it technically doesnt have the right to issue new ids within an identification scheme. HDs which have defined third components (defined UID types) must be unique within the series of IDs defined by that component.
Note: The HD is used in fields that in earlier versions of HL7 used the IS data type. Thus, a single component HD (only the first component valued) will look like a simple IS data type for older systems expecting a single component in the place of the HD data type. If the first component for the HD data type is present, the second and third components are optional. If the third component is present, then the second must also be present (although in this case the first is optional). The second and third components must either both be valued (both non-null), or both be not valued (both null). |
Refer to user-defined table 0300 - Namespace ID for suggested values.
The HDs second component, Universal ID (UID), is a string formatted according to the scheme defined by the third component, Universal ID type (UID type). The UID is intended to be unique over time within the UID type. It is rigorously defined. Each UID must belong to one of the specifically enumerated schemes for constructing UIDs (defined by the UID type). The UID (second component) must follow the syntactic rules of the particular universal identifier scheme (defined by the third component).
The third component governs the interpretation of the second component of the HD. If the third component is a known UID refer to HL7 table 0301 - Universal ID type for valid values, then the second component is a universal ID of that type.
Table 0301 - Universal ID type
Value |
Description |
DNS |
An internet dotted name. Either in ASCII or as integers |
GUID |
Same as UUID. |
HCD |
The CEN Healthcare Coding Scheme Designator. (Identifiers used in DICOM follow this assignment scheme.) |
HL7 |
Reserved for future HL7 registration schemes |
ISO |
An International Standards Organization Object Identifier |
L,M,N |
These are reserved for locally defined coding schemes. |
Random |
Usually a base64 encoded string of random bits. The uniqueness depends on the length of the bits. Mail systems often generate ASCII string "unique names," from a combination of random bits and system names. Obviously, such identifiers will not be constrained to the base64 character set. |
UUID |
The DCE Universal Unique Identifier |
x400 |
An X.400 MHS format identifier |
x500 |
An X.500 directory name |
Note: X400, X500, and DNS are not technically universally valid for all time. Names can be de-registered from an existing user and registered to a new user.
Examples:
1.2.34.4.1.5.1.5.1,1.13143143.131.3131.1^ISO
14344.14144321.4122344.14434.654^GUID
falcon.iupui.edu^DNS
40C983F09183B0295822009258A3290582^RANDOM
LAB1 Local use only: an HD that looks like an IS data type.
PathLab^UCF.UC^L A locally defined HD in which the middle component is itself
structured. This can be considered the combination of
'PathLab' with the locally defined UID system "L".
LAB1^1.2.3.3.4.6.7^ISO An HD with an ISO "Object Identifier" as a suffix, and a
locally defined system name.
^1.2.344.24.1.1.3^ISO An HD consisting only of an ISO UID.