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Version: v0.1.12

Read patient, visit and message details

This guide reads the fields most integrations start with: who the patient is, where they are, and what kind of message arrived. Every example parses the same synthetic admission message.

Read the patient​

msg.patient reads the PID segment. It is undefined when the message has no PID, so use ?..

import { parseHL7 } from "@cosyte/hl7";

const raw = [
  "MSH|^~\\&|CLINIC|MAIN|LAB|REF|20250102153045-0500||ADT^A01^ADT_A01|MSG00001|P|2.5",
  "EVN|A01|20250102153045",
  "PID|1||MRN12345^^^HOSP^MR||Smith^Jane^Q||19800115|F|||123 Main St^^Springfield^IL^62701||^PRN^PH^^^217^5550147",
  "PV1|1|I|ICU^101^A^MAIN||||1234^Welby^Marcus^^^^MD||||||||||||VISIT001",
].join("\r");

const patient = parseHL7(raw).patient;

patient?.mrn; // => "MRN12345"
patient?.fullName; // => "Jane Q Smith"
patient?.familyName; // => "Smith"
patient?.sex; // => "F"
patient?.dateOfBirth?.raw; // => "19800115"
patient?.dateOfBirth?.precision; // => "day"
patient?.address?.city; // => "Springfield"
patient?.address?.zipOrPostalCode; // => "62701"
patient?.identifiers.length; // => 1

mrn is the first PID-3 identifier whose type code is MR, or the first identifier when none is typed MR; identifiers is every PID-3 repetition as a CX composite, always present and possibly empty. A birth date is a fidelity TS that keeps the precision the sender wrote, never a Date (see Read dates and times).

Read the visit​

msg.visit reads PV1, and is undefined when the message has none (most results and orders). location is a PL composite; the doctors are XCN composites.

import { parseHL7 } from "@cosyte/hl7";

const raw = [
  "MSH|^~\\&|CLINIC|MAIN|LAB|REF|20250102153045-0500||ADT^A01^ADT_A01|MSG00001|P|2.5",
  "PID|1||MRN12345^^^HOSP^MR||Smith^Jane^Q||19800115|F",
  "PV1|1|I|ICU^101^A^MAIN||||1234^Welby^Marcus^^^^MD||||||||||||VISIT001",
].join("\r");

const visit = parseHL7(raw).visit;

visit?.patientClass; // => "I"
visit?.location?.pointOfCare; // => "ICU"
visit?.location?.room; // => "101"
visit?.location?.bed; // => "A"
visit?.location?.facility?.namespaceId; // => "MAIN"
visit?.attendingDoctor?.familyName; // => "Welby"
visit?.visitNumber; // => "VISIT001"

Read what kind of message it is​

msg.meta reads the MSH header, with MSH-9 already split into its three components. Branch on messageCode and triggerEvent rather than on type: some senders fill MSH-9.3 and some do not, and type carries it when they do.

import { parseHL7 } from "@cosyte/hl7";

const raw =
  "MSH|^~\\&|CLINIC|MAIN|LAB|REF|20250102153045-0500||ADT^A01^ADT_A01|MSG00001|P|2.5\r" +
  "PID|1||MRN12345^^^HOSP^MR||Smith^Jane^Q";

const meta = parseHL7(raw).meta;

meta.type; // => "ADT^A01^ADT_A01"
meta.messageCode; // => "ADT"
meta.triggerEvent; // => "A01"
meta.messageStructure; // => "ADT_A01"
meta.controlId; // => "MSG00001"
meta.sendingApp; // => "CLINIC"
meta.version; // => "2.5"
meta.timestamp?.offsetMinutes; // => -300

Narrow a message to its type​

msg.is("ADT^A01") makes the same comparison and tells the compiler the answer. Inside the guard the message code and trigger event are literal types, and part and parts accept only the segments that message type's published structure requires.

import { parseHL7 } from "@cosyte/hl7";

const raw =
  "MSH|^~\\&|CLINIC|MAIN|LAB|REF|20250102153045||ADT^A01^ADT_A01|MSG00001|P|2.5\r" +
  "EVN|A01|20250102153045\r" +
  "PID|1||MRN12345^^^HOSP^MR||Smith^Jane^Q";

const msg = parseHL7(raw);

msg.is("ADT^A01"); // => true
msg.is("ADT^A01^ADT_A01"); // => false

if (msg.is("ADT^A01")) {
  const code: "ADT" = msg.meta.messageCode; // a literal type, no longer optional
  code; // => "ADT"
  msg.part("PID")?.field(3).value; // => "MRN12345"
  msg.parts("EVN").length; // => 1
  // msg.part("OBX"); // does not compile: ADT^A01 does not require OBX
  msg.segments("OBX").length; // => 0
}

A key is "<MSH-9.1>^<MSH-9.2>", or the message code alone for a type the published structures match on the code alone ("ACK"). SUPPORTED_OVERLAY_MESSAGES lists every key. Any other string, including the three-component form, returns false and never throws.

Narrowing does not promise presence. An ADT^A01 that arrives without its PID still answers true: part returns undefined and parts an empty list, as segments does, and the absence shows on msg.structure (see Validate a message).

Read a field no helper covers​

A dot-path reaches any field, component or subcomponent: SEGMENT.field.component.subcomponent, numbered from 1 as the standard numbers them. A bracketed index counts from 0.

import { parseHL7 } from "@cosyte/hl7";

const raw = [
  "MSH|^~\\&|CLINIC|MAIN|LAB|REF|20250102153045||ADT^A01|MSG00001|P|2.5",
  "PID|1||MRN12345^^^HOSP^MR~XYZ987^^^STATE^SS||Smith^Jane^Q",
  "NK1|1|Smith^John|SPO",
  "NK1|2|Smith^Ann|DAU",
].join("\r");

const msg = parseHL7(raw);

msg.get("PID.5.1"); // => "Smith"
msg.get("PID.5.2"); // => "Jane"
msg.get("PID.3[1].1"); // => "XYZ987"
msg.get("NK1[1].2.2"); // => "Ann"
msg.getAll("NK1").length; // => 2

The three ways to read a message explains when to reach for a dot-path or for the segment tree instead of a helper.

Reference​