An optimal code for patient identifiers.

How to distinguish 1 billion individuals by an identifier consisting of eight characters, allowing a reasonable amount of error detection or even error correction? Our solution of this problem is an optimal code over a 32-character alphabet that detects up to two errors and corrects one error as well as a transposition of two adjacent characters. The corresponding encoding and error checking algorithms are available for free; they are also embedded as components of the pseudonymisation service that is used in the TMF-the German telematics platform for health research networks.