CDS Hooks on Epic and Cerner: patient-view, order-select, order-sign

Direct answer

patient-view, order-select and order-sign are different workflow points. A card is displayed guidance; a suggestion is an actionable FHIR change. Prefetch is data the EHR may send so the service stays fast.

Hook and card mapping

CDS Hooks is a JSON-over-HTTPS pattern: the EHR (CDS Client) POSTs to {baseUrl}/cds-services/{id} when a named workflow hook fires. Pin the CDS Hooks specification and the hook pages for patient-view, order-select and order-sign. Discovery is GET {baseUrl}/cds-services.

This is not the same article as AI in clinical workflows (model behaviour inside the EHR) or Epic vs Cerner (platform flavour). Both vendors expose CDS Hooks; the hook names and the card schema are the portable contract.

Card versus suggestion versus link:

Prefetch tokens are {{context.patientId}} (and other first-level primitive context fields). Example discovery fragment:

{
  "hook": "order-sign",
  "id": "example-pgx",
  "description": "Example pharmacogenomics check on sign (de-identified).",
  "prefetch": {
    "patient": "Patient/{{context.patientId}}",
    "medications": "MedicationRequest?patient={{context.patientId}}"
  }
}

If required data is in neither prefetch nor an authorized fhirServer, the service responds 412 Precondition Failed. Do not stall the EHR for seconds while you paginate the chart.

Identifier traps

CDS Hooks is decision support plumbing. It is not a licence to give treatment, dosing, or diagnosis. Model output that changes an order still needs a clinician and, where the software is a medical device, a regulatory owner — see the MDR software guide if that question is open.

Test fixtures

De-identified. The Patient id example-p is not a person.

Discovery (truncated):

{
  "services": [
    {
      "hook": "patient-view",
      "id": "static-patient-greeter",
      "title": "Static example",
      "description": "Returns a static info card.",
      "prefetch": {
        "patientToGreet": "Patient/{{context.patientId}}"
      }
    }
  ]
}

patient-view request (truncated):

{
  "hookInstance": "d1577c69-dfbe-44ad-ba6d-3e05e953b2ea",
  "hook": "patient-view",
  "fhirServer": "https://ehr.example.org/fhir",
  "context": {
    "userId": "Practitioner/example-pract",
    "patientId": "example-p",
    "encounterId": "example-enc"
  },
  "prefetch": {
    "patientToGreet": {
      "resourceType": "Patient",
      "id": "example-p",
      "gender": "female",
      "birthDate": "1977-04-12",
      "active": true
    }
  }
}

Info card (no suggestion):

{
  "cards": [
    {
      "summary": "Example info card — not clinical advice.",
      "indicator": "info",
      "source": { "label": "Example CDS Service" },
      "links": [
        {
          "label": "Open example SMART app",
          "url": "https://app.example.org/launch",
          "type": "smart"
        }
      ]
    }
  ]
}

Suggestion shape on order-sign (resource truncated, not a real medication order):

{
  "cards": [
    {
      "summary": "Example: replace the draft order (fixture).",
      "indicator": "warning",
      "source": { "label": "Example CDS Service" },
      "selectionBehavior": "at-most-one",
      "suggestions": [
        {
          "label": "Apply example update",
          "actions": [
            {
              "type": "update",
              "description": "Update the draft ServiceRequest identifier only.",
              "resource": {
                "resourceType": "ServiceRequest",
                "id": "draft-order-1",
                "status": "draft",
                "intent": "order",
                "subject": { "reference": "Patient/example-p" }
              }
            }
          ]
        }
      ]
    }
  ]
}

Minimum tests:

1. patient-view with prefetch present — 200, ≤1 info card, latency budget the EHR actually enforces.
2. patient-view with prefetch key omitted — either 200 with a narrower card or 412; never hang.
3. order-select with two selections — card talks about the selected drafts only.
4. order-sign suggestion accepted vs dismissed (feedback API if the EHR sends it).
5. Same service registered on Epic sandbox and an Oracle Health sandbox — compare draft MedicationRequest required fields.

Failure modes and rollback

Turn a dangerous service off at discovery (remove it from {baseUrl}/cds-services) rather than returning critical cards you cannot support. Rollback is: unregister the hook, keep the EHR workflow native, replay nothing — CDS Hooks is advisory unless you opted into systemActions.

Related service

If you need CDS Hooks wired into Oracle Health / Cerner (and the same cards tested against Epic), that is Cerner integration. For a scoped hook spike, use contact with project intent.

This page is not clinical advice, not a CDS Hooks certification, and not an EHR vendor partnership. Empty cards are a successful response.