Observation.referenceRange field specification
This field follows FHIR BackboneElement, and has following fields
| Key | Type | Always present | Notes | 
|---|---|---|---|
| low | FHIR SimpleQuality | No | Low Range, if relevant | 
| high | FHIR SimpleQuality | No | High Range, if relevant | 
| text | string | No | Text based reference range in an observation |