What Is HL7 v2 OBR-3? Filler Order Number, Explained for Testers
The performing system — a lab, an imaging center — assigns OBR-3 on its own timeline, sometimes only after the order has actually been received and accessioned. Systems that assume it's always populated at order time will choke on early-stage order messages where it's still blank.
OBR-3 is the third field of the HL7 v2 OBR segment — the Filler Order Number, a unique identifier assigned by the performing (filler) system, typically used to key results back to the correct order.
What this field contains
Example
OBR-3 carries FIL98831^SYNTHIB — the filling lab's own order number, distinct from the placer number in OBR-2. Synthetic order — not a real patient.
Where this trips people up
A test suite built entirely from result messages (where OBR-3 is always populated) will never exercise the case where an initial order message goes out with OBR-3 blank, because the filler hasn't accessioned it yet. When that same order is tested end-to-end — placed, then later resulted — a system that requires OBR-3 on the initial order will reject perfectly valid new-order traffic. Test the full order lifecycle, not just the resulted state.