Function: pickMrn()

pickMrn(identifiers): string | undefined

Pick the Medical Record Number string from a list of PID-3 CX identifiers.

D-07: prefer the first CX whose identifierTypeCode === "MR" (HL7 v2.5+ canonical MRN marker). D-10: the match is case-SENSITIVE: lowercase "mr" does NOT match; spec mandates uppercase.

D-08: when no MR-typed identifier is found, fall back to the first CX's idNumber. Returns undefined when the first CX has no idNumber (even if later CXs do: the fallback is strictly "first CX", not "first CX with idNumber", because we need a deterministic answer).

D-21: no warning emitted. Callers who need strict MR resolution can walk patient.identifiers themselves.

Parameters

identifiers

readonly CX[]

Returns

string | undefined

Example

import { pickMrn } from "@cosyte/hl7";
pickMrn([
  { idNumber: "X1" },
  { idNumber: "MRN001", identifierTypeCode: "MR" },
]);
// → "MRN001"

pickMrn([{ idNumber: "X1" }]);
// → "X1"  (fallback: no MR entry)

pickMrn([]);
// → undefined