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201709 LastN Query Track

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Last N Observations Query Track

Submitting WG/Project/Implementer Group

Orders and Observations WorkGroup


The lastn query meets the common need for searching for the most recent or last n=number of observations for a subject.

Examples where this query could be used:

  • Fetch the last 5 temperatures for a patient to view trends
  • Get the most recent lab results for patient
  • Fetch the last 3 results for all vitals for a patient

The $lastn operation is has been introduced as part of FHIR STU3, but has not yet undergone yet been widley implemented. This goal of this track is encourage server implementation of the operation, uncover implementation issues, and help evaluate if similar operations would be useful for other clinical resources such DiagnosticReport.

Proposed Track Lead

Eric Haas

Expected participants


  • Grahame's test server
  • Cerner

Roles & Scenarios


  • Query Requester: Anybody who wants can make an API request
  • Query Responder: FHIR Server

For context roles of the FHIR Query and FHIR Server and Scenarios, refere to the lastn Operation Definition and the examples in the FHIR Specification here

  1. Following the Example in the Specification, requester make an api request to the FHIR server
  2. FHIR server returns the the requested resource Bundle or appropriate error/OperationDefinition
  • This server has a baseURL (see the FHIR specification)
Success Criteria:
  • FHIR Server returns expected resources in bundle as outlined in the speicifiation example
Bonus point:
  • Make additional lastn requests to determine limitations of operation.
  • Extend lastn operation to DiagnosticReport resource (e.g., fetch me the last 3 CBC's for Mrs Smith)