As part of the v2-to-FHIR project we are mapping commonly used fields in key v2 messages to FHIR resources so that messages can be transformed into bundle of FHIR resources. A PRT segment after an OBX segment can be used to indicate the location of the Observation and the date/time of the association of the location to the Observation but there is no sufficient cognate existing data element in FHIR. We suggest that a standard extension to Observation be created to allow exchange of this concept. 

 There is an existing Location extension (http://www.hl7.org/fhir/location.html) but it doesn't allow for begin and end date/times. Either a new complex extension should be created or the existing one extended.