Locate the UM (health care services review information) segment definition in the X12 278 IG; understand UM01 (request category code), UM02 (certification type code), UM03 (service type code), and UM06 (level of service code) as the primary drivers of request classification.
Understand the HI (health care information codes) segment usage in X12 278: HI is used to transmit diagnosis codes (principal diagnosis with qualifier ABK for ICD-10-CM, other diagnoses with ABF) and procedure codes (BK/BO qualifiers for ICD procedure codes).
Locate the HCR (health care services review information) segment in the 278 response: HCR01 carries the action code (certified, not certified, pended), HCR02 carries the authorization/referral number when approved, and HCR03 carries the action code date.
Review the DTP (date or time period) segment usage in 278 loops to understand how service start date, end date, and admission date are transmitted using appropriate DTP01 qualifier codes.
Review the NM1 (individual or organizational name) segment pattern used in each loop to identify payer (PR), subscriber (IL), dependent (QC), rendering provider (82), and service facility (FA) entity identifiers.
Practice constructing a minimal 278 request with a single service line: ISA/GS envelope, ST, HL 2000A-2000F with UM and HI, then the corresponding response with HCR action code A1 (certified).
Known gotchas
UM03 (service type code) uses a narrow set of X12-defined values (e.g., '1' for medical care, 'MH' for mental health) — misidentifying the service type causes payers to route the request to the wrong review unit, leading to inappropriate denials.
HI segments for diagnosis must use the correct qualifier for each diagnosis type (ABK for principal ICD-10-CM, ABF for other ICD-10-CM) — using the wrong qualifier means the payer may not recognize the diagnosis as principal, affecting medical necessity review.
HCR02 (authorization number) is only populated in the response and only when the action code is A1 (certified) — clients must not attempt to extract an authorization number from pended (A4) or denied (A3) responses where HCR02 will be empty.
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp