HL7 v2 PD1-3 (Patient Primary Facility): Format, Values, and Testing Notes
PD1-3 answers a question that MSH can't: not who sent this particular message, but which facility the patient actually considers home base for care. Mix the two up in test data and referral-routing logic never gets a real workout.
PD1-3 is the Patient Primary Facility field, a composite value naming the organization (and optionally an identifier) that the patient is primarily affiliated with for care. It's independent of the sending facility recorded in the message header, and it's most often read by systems deciding where to route referrals or care summaries.
What this field contains
Example
PD1-3 (SYNTHIB COMMUNITY CLINIC^^12345) names the patient's primary facility, independent of whichever facility generated this message.
Where this trips people up
It's common for test fixtures to hardcode PD1-3 to whatever facility is sending the message, since in a single-site test environment the two happen to be identical. That habit means multi-facility routing logic — the code that has to notice a patient's primary facility differs from the encounter facility and act accordingly — stays untested until a real cross-site referral surfaces the gap, usually as a care summary sent to the wrong location.