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Version: v0.2.0

Emit a v2 message from a FHIR resource

Two functions go from FHIR back to v2: toV2Patient builds an ADT message carrying a PID, and toV2Observation builds an ORU message carrying an OBX. Both return { value, issues }, where value is an @cosyte/hl7 message. The path is narrow and lossy by design; Why FHIR to v2 is narrow explains why.

Emit a patient​

You supply the v2 trigger. No FHIR resource carries one, so the library never infers it. Map each identifier system you send to the assigning-authority code the receiver expects, and set the MSH fields in envelope.

import { parseResource } from "@cosyte/fhir";
import { toV2Patient } from "@cosyte/transform";

const { resource } = parseResource(
  JSON.stringify({
    resourceType: "Patient",
    identifier: [{ system: "urn:oid:2.16.840.1.113883.19", value: "MRN12345" }],
    name: [{ family: "Public", given: ["Jane"] }],
    gender: "female",
    birthDate: "1980-01-15",
  }),
);

const { value, issues } = toV2Patient(resource, "A28", {
  assigningAuthorities: { "urn:oid:2.16.840.1.113883.19": "HOSP" },
  envelope: { sendingApp: "EHR", sendingFacility: "MAIN", controlId: "MSG0100" },
});

value?.toString().split("\r")[1]; // => "PID|||MRN12345^^^HOSP||Public^Jane||19800115|F"
issues; // => []

An identifier whose system is not in assigningAuthorities is written with its value and no assigning authority, flagged with TRANSFORM_NO_V2_TARGET rather than invented.

Emit an observation​

import { parseResource } from "@cosyte/fhir";
import { toV2Observation } from "@cosyte/transform";

const { resource } = parseResource(
  JSON.stringify({
    resourceType: "Observation",
    status: "final",
    code: { coding: [{ system: "http://loinc.org", code: "2093-3", display: "Cholesterol" }] },
    valueQuantity: { value: 210, unit: "mg/dL", system: "http://unitsofmeasure.org", code: "mg/dL" },
  }),
);

const { value, issues } = toV2Observation(resource, "R01");

value?.toString().includes("ORU^R01"); // => true
value?.toString().split("\r")[1]; // => "OBX||NM|2093-3^Cholesterol^LN||210|mg/dL^mg/dL^UCUM|||||F"
issues; // => []

The message carries the OBX alone. An Observation names its patient only by reference, and a PID assembled from a reference would be made up.

Check the trigger​

An absent or empty trigger returns no message and TRANSFORM_MISSING_TRIGGER, and nothing is built.

import { parseResource } from "@cosyte/fhir";
import { ISSUE_CODES, toV2Patient } from "@cosyte/transform";

const { resource } = parseResource('{"resourceType":"Patient","gender":"female"}');

const refused = toV2Patient(resource, "");
refused.value; // => undefined
refused.issues[0]?.code === ISSUE_CODES.TRANSFORM_MISSING_TRIGGER; // => true

Check what could not be carried​

Several of the guide's rows map more than one v2 code to the same FHIR code, so going back is ambiguous. FHIR gender other could have come from three v2 codes; the library refuses to pick one and leaves the field empty:

import { parseResource } from "@cosyte/fhir";
import { ISSUE_CODES, toV2Patient } from "@cosyte/transform";

const { resource } = parseResource('{"resourceType":"Patient","name":[{"family":"Public"}],"gender":"other"}');
const { issues } = toV2Patient(resource, "A28");

issues.some((i) => i.code === ISSUE_CODES.TRANSFORM_CODE_NOT_INVERTIBLE && i.v2Location === "PID.8"); // => true

The other refusals work the same way: an element with no v2 field in this map raises TRANSFORM_NO_V2_TARGET, a value v2 cannot carry unchanged raises TRANSFORM_VALUE_NOT_REPRESENTABLE, and a coding system with no v2 mnemonic raises TRANSFORM_CODE_SYSTEM_NOT_V2. Each leaves its field out.

Check the required fields before you send​

A PID needs PID-3 (Patient Identifier List) and PID-5 (Patient Name); an OBX needs OBX-11 (Observation Result Status). None has a safe default. When the resource gives no source for one, the message is still built, the field is left empty rather than filled with a placeholder, and the issues say so with TRANSFORM_V2_REQUIRED_FIELD_ABSENT at error severity:

import { parseResource } from "@cosyte/fhir";
import { ISSUE_CODES, toV2Patient } from "@cosyte/transform";

const { resource } = parseResource('{"resourceType":"Patient","identifier":[{"value":"MRN1"}]}');
const { value, issues } = toV2Patient(resource, "A28");

value?.toString().includes("PID|||MRN1"); // => true
issues[0]?.code === ISSUE_CODES.TRANSFORM_V2_REQUIRED_FIELD_ABSENT; // => true
issues[0]?.v2Location; // => "PID.5"

Add the element to the resource, or repair the message, before it goes out. If nothing in the resource grounds a single field of the segment, there is no message at all, and that is reported as TRANSFORM_NO_V2_MESSAGE_EMITTED rather than returned as an empty success:

import { parseResource } from "@cosyte/fhir";
import { ISSUE_CODES, toV2Patient } from "@cosyte/transform";

const { resource } = parseResource('{"resourceType":"Patient"}');
const { value, issues } = toV2Patient(resource, "A28");

value; // => undefined
issues[0]?.code === ISSUE_CODES.TRANSFORM_NO_V2_MESSAGE_EMITTED; // => true

Reference​