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Wednesday, September 19, 2018

Loving to hate Identifiers

Here's an interesting one.  What's the value set for ObservationInterpretation?  What's the vocabulary?

Well, it depends actually on who you ask, and the fine details are rather weak on their effect in the eventual outcome.

Originally defined in HL7 Version 2, the Observation abnormal flags are defined as content from HL7 Table 0078.  That's HL7-speak for an official table, which has the following OID: 2.16.840.1.113883.12.78.  It looks like this.

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 microbology susceptibilities only:
    S
Susceptible*
    R
Resistant*
    I
Intermediate*
   MS
Moderately susceptible*
   VS
Very susceptible*

When we moved to Version 3 with CDA, we got ObservationInterpretation and it looks something like the following.  It's OID is2.16.840.1.113883.5.83.  The table is even bigger (click the link above) and has a few more values.  But all the core concepts below (found in 2010 normative edition of CDA) are unchanged.

ObservationInterpretation     
One or more codes specifying a rough qualitative interpretation of the observation, such as "normal", "abnormal", "below normal", "change up", "resistant", "susceptible", etc.
LvlType, Domain name and/or Mnemonic codeConcept IDMnemonicPrint NameDefinition/Description
1A: ObservationInterpretationChangeV10214
Change of quantity and/or severity. At most one of B or W and one of U or D allowed.
2  L:  (B)10215Bbetter
Better (of severity or nominal observations)
2  L:  (D)10218Ddecreased
Significant change down (quantitative observations, does not imply B or W)
2  L:  (U)10217Uincreased
Significant change up (quantitative observations, does not imply B or W)
2  L:  (W)10216Wworse
Worse (of severity or nominal observations)
1A: ObservationInterpretationExceptionsV10225
Technical exceptions. At most one allowed. Does not imply normality or severity.
2  L:  (<)10226<low off scale
Below absolute low-off instrument scale. This is statement depending on the instrument, logically does not imply LL or L (e.g., if the instrument is inadequate). If an off-scale value is also low or critically low one must also report L and LL respectively.
2  L:  (>)10227>high off scale
Above absolute high-off instrument scale. This is statement depending on the instrument, logically does not imply LL or L (e.g., if the instrument is inadequate). If an off-scale value is also high or critically high one must also report H and HH respectively.
1A: ObservationInterpretationNormalityV10206
Normality, Abnormality, Alert. Concepts in this category are mutually exclusive, i.e., at most one is allowed.
2  S: ObservationInterpretationNormalityAbnormal (A)V10208AAbnormal
Abnormal (for nominal observations, all service types)
3    S: ObservationInterpretationNormalityAlert (AA)V10211AAAbnormal alert
Abnormal alert (for nominal observations and all service types)
4      L:  (HH)10213HHHigh alert
Above upper alert threshold (for quantitative observations)
4      L:  (LL)10212LLLow alert
Below lower alert threshold (for quantitative observations)
3    S: ObservationInterpretationNormalityHigh (H)V10210HHigh
Above high normal (for quantitative observations)
4      L:  (HH)10213HHHigh alert
Above upper alert threshold (for quantitative observations)
3    S: ObservationInterpretationNormalityLow (L)V10209LLow
Below low normal (for quantitative observations)
4      L:  (LL)10212LLLow alert
Below lower alert threshold (for quantitative observations)
2  L:  (N)10207NNormal
Normal (for all service types)
1A: ObservationInterpretationSusceptibilityV10219
Microbiology: interpretations of minimal inhibitory concentration (MIC) values. At most one allowed.
2  L:  (I)10221Iintermediate
Intermediate
2  L:  (MS)10222MSmoderately susceptible
Moderately susceptible
2  L:  (R)10220Rresistent
Resistent
2  L:  (S)10223Ssusceptible
Susceptible
2  L:  (VS)10224VSvery susceptible
Very susceptible

It's got a value set OID as well.  It happens to be: 2.16.840.1.113883.1.11.78.  Just in case you need more clarification.

Along comes FHIR, and we no longer need to worry about OIDs any more.  Here's the FHIR table.  Oh, and this one is called: http://hl7.org/fhir/v2/0078. That should be easy enough to remember.  Oh, and it has a value set identifier as well: http://hl7.org/fhir/ValueSet/observation-interpretation.  Or is it http://hl7.org/fhir/ValueSet/v2-0078?  

Just to be safe, FHIR also defined identifiers for Version 3 code systems.  So the HL7 V3 ObservationInterpretation code system is: http://hl7.org/fhir/v3/ObservationInterpretation.  Fortunately for us, the confusion ends here, because it correctly says that this code system is defined as the expansion of the V2 value set.

And, so, through the magic of vocabulary, we have finally resolved what Observation interpretation means.  Which leaves us pretty much right back where we started last century.

I'm poking fun of course.  This is just one of the minor absurdities that we have in standards for some necessary but evil reasons that do not necessarily include full employment for vocabularists. The reality is, everyone who needs to knows what these codes mean, and we've been agreeing on them for decades.  We just don't know what to call them.  This is one of those problems that only needs a solution so that we don't look ridiculous.  Hey, at least we got the codes for gender right .. right?  Err, tomorrow maybe.




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