At its core, Observation allows expressing a name-value pair or structured collection of name-value pairs. As such, it can support conveying any type of information desired. However, that is not its intent. Observation is intended for capturing measurements and subjective point-in-time assessments. It is not intended to be used for those specific contexts and use cases already covered by other FHIR resources. For example, the Allergy Intolerance resource represents patient allergies, Medication Statement resource: medications taken by a patient, Family Member History resource: a patient’s family history, Procedure resource: information about a procedure, and Questionnaire Response resource: a set of answers to a set of questions.
The Observation resource should not be used to record clinical diagnosis about a patient or subject that are typically captured in the Condition resource or the Clinical Impression resource. The Observation resource is often referenced by the Condition resource to provide specific subjective and objective data to support its assertions. There will however be situations of overlap. For example, a response to a question of “have you ever taken illicit drugs” could in principle be represented using Medication Statement, but most systems would treat such an assertion as an Observation. In some cases, such as when source data is coming from an Health Level Seven International (HL7) volume two feed, a system might not have information that allows it to distinguish diagnosis, allergy and other “specialized” types of observations from laboratory, vital sign and other observation types intended to be conveyed with this resource. In those circumstances, such specialized observations may also appear using this resource. Adhering to such convention is an appropriate use of Observation. If implementers are uncertain whether a proposed use of Observation is appropriate, they’re encouraged to consult with implementers.