Records medical record number used by the facility to identify the patient.

This number identifies the patient in a facility. It can be used by a central registry to point back to the patient record, and it helps identify multiple reports on the same patient.

UNK	Medical record number unknown
RT	Radiation therapy department patient without HIM number
SU	1-day surgery clinic patient without HIM number

Note: Other standard abbreviations may be used to indicate departments within the facility for patients without HIM numbers assigned.