Many services discover their logging problem on audit day, when it is already too late. A useful audit log must reconstruct who acted, what changed, when it happened, and what the clinical state was at that time.
Seven essential properties.
- Immutability after write.
- Cryptographic integrity or tamper evidence.
- Clear actor identity, not shared service users.
- Trusted timestamps.
- Enough clinical and workflow context.
- Retention aligned with regulation.
- Access to the log is also logged.