X12 healthcare transaction sets

The HIPAA-adopted ASC X12N transaction standards. For each: what it does, which way it flows, and where it shows up in your operation.

The full table

Transaction	Name	Direction	Purpose
270	Eligibility, Coverage or Benefit Inquiry	You → payer	Ask whether a patient is covered and what their cost-share is
271	Eligibility, Coverage or Benefit Response	Payer → you	Coverage status, plan, deductible remaining, copay, coinsurance
276	Health Care Claim Status Request	You → payer	Ask what happened to a submitted claim
277	Health Care Claim Status Response	Payer → you	Claim status
277CA	Health Care Claim Acknowledgment	Payer → you	Accepted into adjudication, or rejected before it
278	Health Care Services Review, Request for Review and Response	Both	Prior authorization / referral certification
820	Payroll Deducted and Other Group Premium Payment	Employer → payer	Premium payment. You’ll rarely see it.
834	Benefit Enrollment and Maintenance	Employer/sponsor → payer	Membership enrollment. Awareness only.
835	Health Care Claim Payment/Advice	Payer → you	Remittance advice, what was paid and why
837P	Health Care Claim: Professional	You → payer	Physician and outpatient claims
837I	Health Care Claim: Institutional	You → payer	Facility claims
837D	Health Care Claim: Dental	You → payer	Dental claims
999	Implementation Acknowledgment	Payer/CH → you	Whether the file was syntactically valid X12
TA1	Interchange Acknowledgment	Payer/CH → you	Whether the interchange envelope was readable
275	Additional Information to Support a Health Care Claim	You → payer	Attachments, where supported

The ones you touch daily

Acknowledgment hierarchy, the distinction that matters

Three responses can come back after you submit an 837, and they mean different things.

	TA1	999	277CA
Level	Interchange envelope	Functional group / transaction syntax	Claim
Answers	Was the envelope readable?	Was the file valid X12?	Did the payer accept the claim into adjudication?
From	Receiver	Clearinghouse or payer	Payer
A rejection means	The file couldn’t be opened	The file was malformed	The payer’s front end refused the claim
Was anything adjudicated?	No	No	No
Appeal rights?	None	None	None

A 277CA rejection is not a denial. Nothing was adjudicated and no determination was made, so there is nothing to appeal. Correct the data and resubmit as a new claim, not as a corrected claim, because there is no original claim in the payer’s system to correct. Conversely, a denial appears in the 835 as a $0 or reduced payment with a denial CARC, and it does have appeal rights. See Claim denials.

Version

Most healthcare transactions currently use the 5010 implementation guides adopted under HIPAA administrative simplification.¹ Version identifiers appear in the GS08 element and the ST03 element, for example 005010X222A1 for the 837P. You will see these strings in error messages. They identify which implementation guide the file claims to follow.

Companion guides

The X12 implementation guide defines required, situational, and optional elements. Payers publish companion guides specifying how they interpret the situational and optional parts, what identifiers they expect, how they want files delivered, and what their front-end edits check. This is why two payers can both be fully standards-compliant and still reject each other’s accepted claims, and it is the variation your clearinghouse absorbs. See What is a clearinghouse?.

Where each transaction shows up

Operational moment	Transaction
Booking an appointment	270 → 271
Check-in re-verification	270 → 271
Requesting prior authorization	278, or a portal, or fax
Submitting the claim	837P / I / D
Overnight rejection review	999, 277CA
Chasing an unpaid claim	276 → 277
Posting payments	835
Reconciling a deposit	835 `TRN` segment, matched to the EFT’s ACH addenda

The ones to build against

If you are building automation, these are where the value is:

Transaction	Automation opportunity
270/271	Batch eligibility for tomorrow’s schedule; auto-flag exceptions; drive point-of-care estimates
835	Denial analytics by CARC, payer, and entity; underpayment detection against loaded fee schedules
277CA	Same-day rejection alerting
276/277	Automated status chasing on aged claims

Doing any of this requires programmatic access to the transactions, which is a clearinghouse selection criterion rather than an EHR one. API-first clearinghouses expose these as JSON as well as X12; batch-era vendors generally do not. See Choose a clearinghouse.

PHI

837, 835, 271, and 277 files all contain protected health information: names, member IDs, dates of service, diagnosis and procedure detail. Encrypt in transit and at rest, access-control them, and cover any analytics store in your BAAs and your security risk analysis. See HIPAA for MSO-PC operators.

Sources

HIPAA administrative simplification, 45 C.F.R. pts. 160, 162. CMS, Administrative Simplification: Transactions. Standards maintained by ASC X12.

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Glossary & Appendices

X12 healthcare transaction sets

The full table

The ones you touch daily

Acknowledgment hierarchy, the distinction that matters

Version

Companion guides

Where each transaction shows up

The ones to build against

PHI

Sources

​The full table

​The ones you touch daily

​Acknowledgment hierarchy, the distinction that matters

​Version

​Companion guides

​Where each transaction shows up

​The ones to build against

​PHI

​Sources

The full table

The ones you touch daily

Acknowledgment hierarchy, the distinction that matters

Version

Companion guides

Where each transaction shows up

The ones to build against

PHI

Sources