The short answer
A patient record migration is judged on the records that do not fit the model: incomplete ones, duplicated people, historical formats, records attached to staff who left. Those are a small proportion and most of the work.
Plan for staged migration with verification at each stage, and keep read access to the source system well past cutover.
Where migrations break
| Problem | Why it is hard |
|---|---|
| Duplicate patients | Merging is a clinical decision, not a technical one |
| Incomplete records | Target system may require fields the old one did not |
| Free text notes | Meaning is not structured and cannot be inferred safely |
| Attachments | Often stored separately, easily orphaned |
| Historical coding | Code sets change over time |
Duplicates are the one to raise early. Deciding whether two records are the same person is a clinical and governance decision, and it cannot be delegated to a matching rule alone.
Verify against the source
- Count records in the source, the export and the target, and reconcile the differences deliberately.
- Sample records across categories, including the awkward ones, and compare field by field.
- Verify attachments resolve, not just that references exist.
- Have clinical staff review a sample in the new system, in their normal workflow.
- Record every deliberate exclusion with the reason.
Verifying against the export rather than the source hides anything the export itself dropped, which is a common and expensive class of failure.
Keep the old system readable
Plan for read access to the source system for a long period after cutover, longer than feels necessary. Questions about historical records surface for months, and the answer cannot be that the data is gone.
If the old system cannot be kept running, produce a complete, readable archive before decommissioning and confirm someone can actually open and search it.
Governance is part of the project
Record retention, access controls, audit logging and the lawful basis for processing all need addressing as part of the migration rather than afterwards.
Involve whoever is accountable for information governance from the start. Retrofitting an audit trail onto a migrated system is considerably harder than building it in.