X12 278 — Health Care Services Review

Prior-authorization (pre-certification, referral) request sent by a provider to a payer, and the payer's response carrying the decision.

Purpose

The 278 asks the payer to approve a service ahead of time when it is expensive or regulatorily scoped: scheduled surgery, MRI, CT scan, inpatient stay, medical transport, specialty therapy… Without a favourable 278 the matching 837 claim is usually denied. The 278 also supports referrals (specialist routing) and admission notifications.

Envelope and structure

The 278 uses the standard triple X12 envelope with GS01 = HI. The TR3 in ST03 distinguishes Request (005010X217) from Inquiry (005010X216). Example pre-auth for a surgical procedure:

ISA*00*          *00*          *ZZ*PROVIDER01     *ZZ*PAYER99        *260513*1400*U*00501*000000278*0*P*>~
GS*HI*PROVIDER01*PAYER99*20260513*1400*1*X*005010X217~
ST*278*0001*005010X217~
BHT*0007*13*REQ-AUTH-001*20260513*1400~
HL*1**20*1~
NM1*X3*2*PAYER99*****PI*PAYER99~
HL*2*1*21*1~
NM1*1P*2*ACME CLINIC*****XX*1234567890~
HL*3*2*22*1~
TRN*1*TRACE-AUTH-001*9PROVIDER01~
NM1*IL*1*DOE*JANE****MI*MEMBER12345~
DMG*D8*19850412*F~
HL*4*3*EV*0~
UM*HS*I*4*11:B~
DTP*AAH*RD8*20260520-20260520~
HI*BK:M5435~
SE*14*0001~
GE*1*1~
IEA*1*000000278~

Common segments (concept)

• Header — BHT with purpose 13 (request). Hierarchical HL loops: 2000A Utilization Management Organization (payer), 2000B Requester (provider), 2000C Subscriber, and 2000E Service Event.
• Detail — UM Health Care Services Review Information carries the service request type (HS Health Services Review, SC Specialty Care Review…), the request category, the service line, and the facility type. HI Health Care Information Codes carries diagnosis codes (ICD-10). DTP Date or Time or Period defines the planned service window, and HCR Health Care Services Review (in the response) carries the decision: A1 Certified in Total, A4 Modified, A6 Pended, etc.
• Summary — a single SE.

When you'll see it

The 278 is the #1 friction point in the US patient journey: a pre-auth round-trip can take 24 hours to several days depending on the service and payer, with significant API-quality variance across payers. Specialised vendors (Cohere Health, Olive AI, Surescripts) build orchestration layers on top of the 278 to automate criteria checking and cut administrative denials. CMS-0057-F (effective early 2026) additionally requires a FHIR Prior Authorization API alongside the 278 EDI flow.

Related transactions

• 270 / 271 — Eligibility check that often precedes the 278. 270 · 271
• 837 — The claim that will follow the authorization. See 837 page →
• 275 — Additional Information (document upload to payer).
• 999 — Implementation Acknowledgment. See 999 page →

Documentation

• x12.org/products/transaction-sets — public index, name and code 278.
• stedi.com/edi/x12/transaction-set/278 — public editorial reference, examples.
• cms.gov — HIPAA EDI guides .
• TR3 005010X217 and 005010X216 — available for purchase on x12.org or via DISA.