How to Document an HL7 Interface (Template + Checklist)

Ask any healthcare integration engineer where their interface documentation lives and you'll usually get an uncomfortable pause. It's in a spreadsheet. It's in a Word doc from three interfaces ago. It's in someone's head — and that someone is on vacation.

Interface documentation is the first thing everyone agrees is important and the first thing that gets skipped under deadline pressure. This post gives you a concrete template and checklist so it stops being an afterthought.

Why HL7 interface documentation matters

Key-person risk. If one engineer holds the details of how your ADT feed maps to your EHR, their departure is an outage waiting to happen.
Faster troubleshooting. When a message fails at 2am, good documentation is the difference between a five-minute fix and a five-hour investigation.
Onboarding. New interface analysts get productive in days, not months, when the existing interfaces are actually written down.
Vendor and audit conversations. Clear documentation makes every external conversation — with the EHR vendor, the lab, the auditor — dramatically shorter.

What to capture: the checklist

For every interface, document:

1. The endpoints

Source system and destination system (name, version, owner)
Connection details: protocol (MLLP, TCP, file, API), host/port concept — never put secrets in documentation
Environment: production vs test

2. The message profile

Message types (ADT^A01, ORM^O01, ORU^R01, etc.)
HL7 version (2.3, 2.5.1, etc.)
Trigger events and expected volume

3. The mapping

Field-level mappings: which source segment/field maps to which destination segment/field (e.g. MSH-4 to facility code)
Transformations and value translations (code sets, defaults, formatting)
Filtering rules: which messages are dropped or routed differently

4. The operational details

Acknowledgement mode (original vs enhanced, when ACK/NAK is sent)
Error handling and retry behavior
Alerting: who gets notified when it breaks

5. The context

Why this interface exists (the clinical or business reason)
Known quirks and gotchas
Change history

A simple template

Interface: [Source] -> [Destination]
Purpose: [one line]
Owner: [team/person]

Endpoints
  Source:      [system, version]
  Destination: [system, version]
  Protocol:    [MLLP/TCP/file/API]  Environment: [prod/test]

Messages
  Types:   [ADT^A01, ...]
  Version: [2.5.1]
  Volume:  [~N/day]

Mapping
  [source field] -> [destination field]  | [transformation notes]
  ...

Operations
  ACK mode:       [...]
  Error handling: [...]
  Alerting:       [...]

Notes / gotchas
  - ...

The real problem: keeping it up to date

The hard part isn't writing documentation once — it's keeping it in sync as the interface changes. Documentation that lies is worse than no documentation.

This is exactly why we built Radinode. Instead of maintaining a separate document that drifts from reality, you map the integration once as a visual workflow — endpoints, message types, field mappings, transformations — and Radinode generates the technical guide as a clean PDF automatically. Change the workflow, regenerate the guide. It also exports Mirth-ready artifacts and HL7/FHIR from the same source of truth, so your documentation and your implementation never diverge.

If you're documenting interfaces by hand today, see how Radinode does it in minutes.