Hi all 
I would like to have more granular control of an Observation.category, differentiating within the laboratory code (e.g. biochem vs haematology). Is there a widely accepted coding system for this? Although it’s possible to inspect the Observation.code, my particular use case would be made much easier by simply requiring a second / alternate category.
I think I may have found my own answer, so will share it in case others have a similar use case.
The Diagnostic Service Section Codes are used as an example for DiagnosticReport.category and provide sufficient granularity.
Side note: this does raise a concern regarding consistency (e.g. a Chemistry DiagnosticReport with a vital-sign Observation).
The existing preferred Observation.category is a high level categorization. There is a continuum from this categorization valueset to more and more granular categorizations until becomes equivalent to Observation.code. There aren;t many other categorization out there that cover stuff outside of lab. but for lab sould start with the LOINC Classes.
“Side note: this does raise a concern regarding consistency (e.g. a Chemistry DiagnosticReport with a vital-sign Observation)”
This is typically a concern when searching based on category. IF DR has several categories could contain >1 categories in the latest ver of FHIR.
Thanks Eric