Query: When was my last drug abuse screening test?, FHIR Resource: {'resourceType': 'Observation', 'status': 'final', 'category': [{'coding': [{'system': 'http://terminology.hl7.org/CodeSystem/observation-category', 'code': 'laboratory', 'display': 'Laboratory'}]}], 'code': {'coding': [{'system': 'http://loinc.org', 'code': '5787-7', 'display': 'Epithelial Cells'}], 'text': 'Epithelial Cells'}, 'subject': {'reference': 'urn:uuid:aee1221c-0e31-c34b-cba4-76fa6a75da5a'}, 'effectiveDateTime': '2017-02-21T10:29:18+05:30', 'valueQuantity': {'value': 3.2045, 'unit': '/[HPF]', 'system': 'http://unitsofmeasure.org', 'code': '/[HPF]'}, 'interpretation': None}