HL7 Table HL70074: Diagnostic Service Section ID

HL70074 classifies the clinical service section that produced an order or result. It is the single-most-loaded code table on the OBR segment, populated on every laboratory, radiology, cardiology, and ancillary diagnostic message, and is the field downstream EHRs and analytics systems use to route results to the right inbox, the right worklist, and the right chart tab. Forty-two codes are defined in v2.8.1, drawn from the ID data type.

Purpose

HL70074 answers a routing question: which diagnostic service section produced this order or owns this result. It is not a CPT code, not a LOINC code, not a department billing code — it is a coarse-grained section label (Chemistry, Microbiology, Radiology, Audiology) that helps a receiving system file the message under the right service line without parsing the underlying result codes.

Because the table is HL7-defined, every conformant v2 receiver is expected to recognize all forty-two codes without local extension. Sites that need a finer-grained section (e.g., separating special chemistry from routine chemistry) carry that distinction in a different field — typically a local OBR-25 extension or a sending-facility-scoped code on OBX-3 — rather than overloading HL70074.

Where it's used

OBR-24 Diagnostic Service Section ID — the canonical home of HL70074, populated on every ORM, ORU, OUL, and OML message that carries a diagnostic order or result.
OBR-24 is the field that drives DiagnosticReport.category in v2-to-FHIR mappings.

Code list

Code	Display	Comment/Description
AU	Audiology	Hearing assessment and related audiometric studies.
BG	Blood Gases	Arterial and venous blood gas panels.
BLB	Blood Bank	Transfusion service — type and screen, crossmatch, antibody workup.
CG	Cytogenetics	Karyotype, FISH, chromosomal microarray.
CH	Chemistry	Routine and special clinical chemistry.
CP	Cytopathology	Pap smears, fine-needle aspirate cytology.
CT	CAT Scan	Computed tomography imaging.
CTH	Cardiac Catheterization	Coronary angiography and interventional cardiology.
CUS	Cardiac Ultrasound	Echocardiography.
EC	Electrocardiac (e.g., EKG, EEC, Holter)	Twelve-lead ECG, Holter, event monitor.
EN	Electroneuro (EEG, EMG, EP, PSG)	Electroencephalography, electromyography, evoked potentials, polysomnography.
GE	Genetics	Molecular genetic testing — gene panels, sequencing.
HM	Hematology	CBC, differential, coagulation.
ICU	Bedside ICU Monitoring	Continuous bedside physiologic monitoring data.
IMG	Diagnostic Imaging	Generic imaging when a more specific modality code does not apply.
IMM	Immunology	Autoantibody, complement, immunoglobulin testing.
LAB	Laboratory	Generic laboratory when a finer section code is unknown.
MB	Microbiology	Bacteriology — culture and sensitivity, gram stain.
MCB	Mycobacteriology	AFB smear and culture.
MYC	Mycology	Fungal culture and identification.
NMR	Nuclear Magnetic Resonance	MRI imaging.
NMS	Nuclear Medicine Scan	Nuclear medicine — bone scan, MUGA, PET.
NRS	Nursing Service Measures	Nursing-collected observations and assessments.
OSL	Outside Lab	Results sent in from a reference lab outside the reporting facility.
OT	Occupational Therapy	OT evaluation and treatment notes.
OTH	Other	Section that does not fit any of the other codes.
OUS	Obstetric Ultrasound	OB sonography.
PF	Pulmonary Function	Spirometry, lung volumes, diffusion capacity.
PHR	Pharmacy	Pharmacy-sourced observations (TDM levels reported by pharmacy, etc.).
PHY	Physician (Hx. Dx, admission note, etc.)	Physician-authored narrative results — H&P, admission note, consult.
PT	Physical Therapy	PT evaluation and treatment notes.
RAD	Radiology	Plain-film and general radiology.
RC	Respiratory Care (therapy)	Respiratory therapy treatments and assessments.
RT	Radiation Therapy	Radiation oncology treatment planning and delivery.
RUS	Radiology Ultrasound	General radiology ultrasound (non-cardiac, non-OB, non-vascular).
RX	Radiograph	Plain radiograph.
SP	Surgical Pathology	Tissue biopsy and resection specimen pathology.
SR	Serology	Infectious-disease serology.
TX	Toxicology	Drug screens, therapeutic drug monitoring, heavy-metal panels.
URN	Urinalysis	Routine and microscopic urinalysis.
VR	Virology	Viral culture, antigen, and PCR testing.
VUS	Vascular Ultrasound	Duplex and arterial-venous Doppler studies.
XRC	Cineradiograph	Dynamic cine radiography (swallow studies, GI motility).

Code system OID

OID: 2.16.840.1.113883.18.24
Canonical URI: http://terminology.hl7.org/CodeSystem/v2-0074

The OID resolves on the HL7 Terminology server and is the value Vorro emits in CWE.14 when a downstream v2.7+ profile demands OID-bound coded values on OBR-24.

HL7-defined vs user-defined

HL70074 is HL7-defined. The table number falls inside the HL7-reserved range (HL70001–HL70999), and the code set is normative — receivers must accept all forty-two codes without local extension. Sites that need a finer-grained section (special chemistry vs. routine chemistry, MRI sub-modalities, etc.) do not extend HL70074; they carry the distinction in a separate locally-scoped field or in the OBX-3 result code.

Version differences

v2.1 – v2.2 — Core lab sections only: CH, HM, MB, SR, BG, URN, RAD, NMR, NMS, plus OTH.
v2.3 — Cardiology and neurodiagnostic codes added (EC, EN, CTH, CUS).
v2.3.1 — Imaging codes expanded (CT, IMG, OUS, RUS, VUS, XRC).
v2.4 — Therapy codes added (OT, PT, RC, RT) and pharmacy (PHR), physician narrative (PHY).
v2.5 — Cytogenetics (CG), genetics (GE), mycology (MYC), mycobacteriology (MCB), virology (VR) added.
v2.6 – v2.8.1 — Set frozen at forty-two codes; no further additions.

Common mistakes

Using LAB as a default when a more specific section code exists. LAB is meant as a fallback when the producing section is genuinely unknown; routing engines downstream cannot demultiplex LAB into chemistry vs. hematology vs. microbiology.
Confusing RAD and IMG. RAD is plain-film radiology; IMG is the generic imaging fallback. CT, MR, and US have their own codes.
Sending CH for a hematology result. HL70074 separates chemistry (CH) from hematology (HM) — they file to different worklists in most EHRs.
Sending lowercase or display strings — chemistry instead of CH. OBR-24 is ID data type and case-sensitive.
Treating HL70074 as a billing code. It is a routing label; CPT and revenue codes live on FT1 and IN1.

Examples

A routine chemistry OBR with HL70074 = CH:

OBR|1|123456^EPIC|789012^LAB|24323-8^Comprehensive metabolic 2000 panel^LN|||20260601120000||||||||^^^^^DOC||||||20260601130000|||F||||||||CH

A radiology OBR with HL70074 = RAD:

OBR|1|987654^EPIC|345678^RAD|36643-5^Chest X-ray 2 views^LN|||20260601140000||||||||^^^^^DOC||||||20260601145000|||F||||||||RAD

A microbiology result routed via MB:

OBR|1|555111^EPIC|222333^LAB|600-7^Bacteria identified in Blood by Culture^LN|||20260601090000||||||||^^^^^DOC||||||20260603160000|||F||||||||MB

Same CH value translated to a FHIR DiagnosticReport.category snippet:

{
  "resourceType": "DiagnosticReport",
  "category": [{
    "coding": [{
      "system": "http://terminology.hl7.org/CodeSystem/v2-0074",
      "code": "CH",
      "display": "Chemistry"
    }]
  }]
}

Mapping failure example — unknown vendor extension:

OBR|1|123|456|...|||||||SPCHEM

SPCHEM (special chemistry) is not in HL70074. A conformant engine should route the message to a curation queue, preserve the original SPCHEM in the audit log, and either remap to CH with an extension that preserves the local sub-section or pass through with a soft warning.

FHIR mapping

The v2-to-FHIR IG does not publish a ConceptMap for this table; the mapping below follows the obvious correspondence: the FHIR target ValueSet http://terminology.hl7.org/ValueSet/v2-0074 mirrors HL70074 directly — every v2 code has an exact FHIR counterpart with the same code value. The mapping does not collapse codes, so round-tripping OBR-24 through DiagnosticReport.category is loss-less.

DiagnosticReport.category is CodeableConcept (0..*), allowing multiple section labels per report. Implementations that need both HL70074 and a local section taxonomy can carry both codings in the same array.

Engine considerations

Two- and three-character validation — OBR-24 may be 2 or 3 characters (BLB, CTH, CUS, ICU, IMG, IMM, MCB, MYC, NMR, NMS, NRS, OSL, OTH, OUS, PHR, PHY, RUS, URN, VUS, XRC). Engines must not truncate to two characters.
Case sensitivity — HL70074 codes are case-sensitive uppercase; ch is not valid. Normalize on ingest.
CWE upgrade path — In v2.7+ profiles OBR-24 may be transmitted as CWE rather than ID, allowing OID metadata in CWE.14 (2.16.840.1.113883.18.24). Engines must handle both shapes.
Default fallback — When the source system cannot identify a specific section, prefer LAB over OTH for laboratory results; OTH should be reserved for genuinely non-laboratory, non-imaging sections.
Round-trip preservation — When mapping to FHIR DiagnosticReport.category, preserve the original HL70074 code in the Coding so the outbound v2 channel can restore OBR-24 exactly.

How Vorro handles HL70074

Vorro validates OBR-24 against the forty-two HL70074 codes on ingest. Values that match are forwarded to all downstream channels untouched. Values that fail validation — including lowercase variants, vendor extensions, and accidental display strings — are routed to the terminology curation queue, where they either resolve to one of the forty-two canonical codes (and a remap rule is created) or pass through with a soft warning so downstream systems are not silently fed bad data.

On outbound, Vorro emits HL70074 as ID for v2.5 and earlier profiles and as CWE with CWE.14 populated for v2.7+ destinations that advertise OID-bound coded values. The original HL70074 code is always preserved when round-tripping through FHIR DiagnosticReport.category.

Sources

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