HL7 v2 OBR-4 (Universal Service Identifier): Format, Values, and Testing Notes
OBR-4 tells a downstream system what was actually ordered — a CBC, a chest X-ray, a specific panel. When the coding system used in OBR-4 doesn't match what the receiving system's order catalog expects, orders land in an 'unrecognized test' queue instead of routing automatically.
OBR-4 is the fourth field of the HL7 v2 OBR segment — the Universal Service Identifier, a coded value plus text name that identifies the specific test, panel, or procedure being requested.
What this field contains
Example
OBR-4 carries CBC^Complete Blood Count^L — a locally coded test identifier with its text name. Synthetic order — not a real patient.
Where this trips people up
It's common to see an ordering system send OBR-4 with local codes (coding system L) while the receiving lab's catalog is built around LOINC. If the interface only maps on the identifier component and ignores the coding-system component, a local code that happens to collide numerically with an unrelated LOINC code will route the order to the wrong test. Mapping tables need to key on identifier plus coding system together, never the identifier alone.