Observation Reference Range - How is this being implemented in the UK?

Observation. ReferenceRange
Most observations only have one generic reference range. Systems MAY choose to restrict to only supplying the relevant reference range based on knowledge about the patient (e.g., specific to the patient’s age, gender, weight and other factors), but this might not be possible or appropriate. Whenever more than one reference range is supplied, the differences between them SHOULD be provided in the reference range and/or age properties.

I’m interested in how this is implemented?

I don’t believe this has been discussed.

You can describe reference ranges in ObservationDefinition - FHIR v4.0.1
in qualifiedInterval. If this was available would you include the reference range used in the Observation?

I recently worked on HL7v2 lab results to FHIR and we used what was supplied in the ORU_R01 message (a simple range).

This discussion may be useful https://chat.fhir.org/#narrow/stream/179166-implementers/topic/How.20to.20associate.20an.20Observation.20with.20ObservationDefinition.3F