X12 for billers

A field guide to the X12 segments you will run into when reading the Submission tab or the receivable Trace tab — without leaving the billing manual for the full EDI manual.

How an X12 file is shaped

ISA*...                ← envelope start
  GS*...               ← functional group
    ST*837*...         ← transaction set start
      BHT*...
      HL*...           ← hierarchy
        loops
      SE*...           ← transaction set end
    ST*...
  GE*...               ← functional group end
IEA*...                ← envelope end

You will rarely need to read these. When the Submission tab says a file rejected at TA1 (envelope) vs 999 (transaction parsing), this shape is what's at issue.

837 — claim out

The bones of a professional claim:

Loop	Segment	Field
2010BA	`NM1IL1<lastname>...`	Subscriber demographics.
2010BB	`NM1PR2<payer>...`	Payer name.
2300	`CLM<icn><amount>*...`	Claim header.
2300	`DTP*431/432/096`	Onset / accident / discharge dates.
2300	`HIABK<dx>`	Principal dx.
2300	`REF9F<auth>`	Auth reference.
2310B	`NM1821*<rendering provider>`	Rendering provider.
2400	`LX*1`	Service line counter.
2400	`SV1HC:<cpt>:<mods>...`	Service line (P).
2400	`DTP472D8*<DOS>`	Date of service.
2400	`REF6R<line ref>`	Line item ref.

Institutional (837I) has different shape — SV2 instead of SV1, revenue codes, OCC / VAL / CON segments.

999 — file ack

Segment	Field
`AK1`	Functional group ack header.
`AK2`	Transaction ack header.
`IK3`	Bad segment.
`IK4`	Bad element.
`IK5`	Transaction status (`A` accept, `E` accept w/ errors, `R` reject).
`AK9`	Functional group status.

A 999 rejection means the file structure failed. Almost always: delimiters, envelope IDs, control number mismatch.

277CA — claim ack

Segment	Field
`STC<status>...`	Status code (e.g. `A1`, `A7`, `R7`).
`REF1K<payer claim control>`	Payer's claim ID.
`DTP472D8*<DOS>`	Service date.
`QTY90<count>`	Count of accepted/rejected lines.

STC01's first character: A = acknowledged, R = rejected, E = error. The full code (A7, R7) carries the reason.

835 — remittance

Segment	Field
`BPR<I/C><amount>*...`	Payment header. I = check, C = ACH, etc.
`TRN1<trace>*<payer ID>`	Transaction trace.
`N1PR<payer name>`	Payer.
`N1PE<payee name>`	Payee.
`LX*<counter>`	Loop counter.
`CLP<patient acct><status><billed><paid><patient resp><filing code>*<icn>`	Claim level.
`CAS<group><reason>*<amount>`	Claim-level adjustment.
`NM1QC<patient last><first>...`	Patient.
`SVCHC:<cpt>:<mods><billed><paid><rev code>*<units>`	Service line.
`DTM150<from>` / `151*<to>`	Service date range.
`CAS<group><reason>*<amount>`	Line-level adjustment.
`LQHE<RARC>`	Remark code.
`AMTF2<amount>`	Allowed amount (line).
`AMTB6<amount>`	Allowed amount (service).
`PLB<provider id><date><reason>:<ref>*<amount>`	Provider-level adjustment (file footer).

CAS group codes

Group	Meaning	Routes to
`CO`	Contractual	Contractual write-off.
`PR`	Patient responsibility	Patient AR.
`OA`	Other	Various.
`CR`	Reversal	Reverses a prior CAS.
`PI`	Payer-initiated	Various.

270 / 271 — eligibility

Segment (271)	Field
`EB<status><service code><level><plan>`	Eligibility benefit.
`EB01`	`1` Active, `2` Active full risk, `6` Inactive, etc.
`DTP291<from>` / `292*<to>`	Plan begin / end.
`MSG*<text>`	Free-text.

276 / 277 — claim status

Segment (277)	Field
`STC<status><date>*<amount>`	Status.
`REF1K<payer ICN>`	Reference.
`DTP472D8*<DOS>`	Service date.
`QTY90<count>`	Count.

STC01 family codes are described in 3.2 — Track acks and 6.4 — Claim status inquiry.

278 — authorization

Segment	Field
`UM<request category><certification type>*<service type>`	Auth request.
`HSD<units><count>*<period>`	Service limits.
`REFBB<auth #>`	Auth number (response).
`DTP291<from>` / `292*<to>`	Effective dates.

How the platform helps you not read this

The Submission tab and the Trace tab decode segments inline:

Hover any segment chip → human description.
Click → expanded structured view.
The auto-decode covers the segments above plus less-common ones.

Reach for the EDI Manual when:

You're authoring or fixing a companion guide.
You need to defend an interpretation against the payer.
You're debugging an envelope-level reject.

For day-to-day work, the platform's structured view is enough.

How an X12 file is shaped​

837 — claim out​

999 — file ack​

277CA — claim ack​

835 — remittance​

CAS group codes​

270 / 271 — eligibility​

276 / 277 — claim status​

278 — authorization​

How the platform helps you not read this​