Question: Positional location of OBX-3 codes and AS 4700.2

May 21, 2013

Question:

I have LOINC codes in OBX.3-1, OBX.3-2, OBX.3-3 for most of my results and then I have a result that I have no LOINC code for. Do I place a local code in OBX.3-1, OBX.3-2, OBX.3-3 or do I leave them blank and put it in OBX.3-4, OBX.3-5, OBX.3-6?

e.g. usually it would be this:

2896-8^SODIUM^LN^K^SODIUM^NATA[NNN]

and should I have

WEIRD^MY WEIRD TEST^NATA[NNN]

or

^^^WEIRD^MY WEIRD TEST^NATA[NNN]

Answer:

OBX-3 is of type CE. in v2.4 (AS 4700.2 is based on v2.4), the CE data type definitions says:

Components 4..6 are defined analogously to components 1..3 for the alternate or local coding system. If the alternate text component is absent, and the alternate identifier is present, the alternate text will be taken to be the same as the text component. If the alternate coding system component is absent, it will be taken to mean the locally-defined system

OBX-3, on the other hand, says:

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). LOINC® is an HL7 approved code system for the Observation identifier.

That’s kind of a dollar each way then, as to whether the locally defined code system goes in 1-3 or 4-6. In the context of AS 47002, this is cleared up by the implementation handbook, which says:

Example: LOINC: |6300-8^Glucose^LN| ‘LN’ is the HL7 indicator code for LOINC Local: |Na^Sodium^NATA1234| 1234 is the NATA# for a laboratory. Local: |Na^Sodium^NATA1234-7| Ditto except using version 7 method or format Laboratories may provide both the local and the LOINC codes and descriptions.

…

Important: Where a code is available from a public terminology such as LOINC or SNOMED-CT and a local code the public terminology should come first as in the example above. Where both a LOINC and SNOMED code is sent then the LOINC code has to be in the 1st triplet. Where two codes are sent they must be codes for the same concept. (from 13.21)

So the answer is definitely to place the local code in components 1-3 when there is no LOINC code.