A physician who had just bought out her retiring partner sat in on her first billing meeting as the owner. The biller said the 837s went out Tuesday, the 999s were clean, but a batch had 277CA rejections from one payer, and the 835s from another payer had not posted because the enrollment was pending. The physician nodded and later admitted she had understood about a third of it. She is not alone. These file names are the daily vocabulary of billing and the daily mystery of everyone else in the practice.
The vocabulary comes from HIPAA. The law's administrative simplification provisions require payers and providers to use standard electronic formats for common transactions, and the standards are numbered by the committee that maintains them. Each number is a type of file with a defined job. Once you know the six or seven that a practice touches, the billing meeting makes sense, and, more usefully, you know which report to ask for when money is stuck.
So here are the EDI transactions explained in the order a claim meets them, with what each one carries, where it fails, and what to look at. A glossary line first: EDI is electronic data interchange, the structured exchange of business documents between computer systems. A clearinghouse is the intermediary that receives your files, checks them, translates them into each payer's preferred format, and routes the responses back.
Key takeaways
- The 270/271 pair is eligibility; the 837 is the claim; the 999 and 277CA are acknowledgements; the 276/277 is claim status; the 835 is payment and remittance.
- A claim can fail at three checkpoints before adjudication (the clearinghouse scrubber, the 999 syntax check, and the 277CA payer acceptance), and each has its own report.
- The 277CA is the most neglected file in most practices and the source of most "we never heard back" claims.
- ERA and EFT enrollment are separate steps with each payer, and a missing 835 enrollment means posting by hand from paper.
- Every transaction has an identifier that ties it to the others; learning to follow those identifiers is what makes a claim traceable.
The EDI transactions in the order a claim meets them
| Transaction | Direction | What it carries | Where it fails |
|---|---|---|---|
| 270 / 271 | Practice asks, payer answers | Eligibility inquiry and response: coverage active, plan, copay, deductible remaining, other coverage | Wrong member ID or date of birth; payer returns a generic active status with no benefit detail |
| 278 | Practice asks, payer answers | Authorization or referral request and response | Payer does not support it electronically; most authorizations still go through portals |
| 837P (and 837I) | Practice to payer | The professional claim (837P) or institutional claim (837I): patient, provider, diagnosis, procedure lines, charges | Missing or invalid data at the clearinghouse scrubber |
| 999 | Payer or clearinghouse to practice | Acknowledgement that the 837 file was syntactically valid, or rejection of the whole file or a claim within it | File-level rejections that take down every claim in the batch |
| 277CA | Payer to practice | Claim acknowledgement: each claim accepted into adjudication with a payer claim number, or rejected with a reason | Payer front-end edits: provider not enrolled, member not found, duplicate |
| 276 / 277 | Practice asks, payer answers | Claim status inquiry and response: pending, finalized, paid, denied | Payer supports it but the practice never uses it, so status is checked by phone |
| 835 | Payer to practice | Electronic remittance advice: what was paid, denied and adjusted, with reason codes, plus provider-level adjustments | ERA enrollment not completed; 835 arrives but does not match to claims in the system |
There is also the EFT, the electronic funds transfer, which is the money itself moving to your bank account. The EFT and the 835 are separate; they share a trace number so the payment can be matched to the remittance. Practices that receive EFTs without 835s (because ERA enrollment was never completed) end up posting from paper or the portal, which is the slowest and most error-prone way to do it.
270/271: the eligibility check
The 270 is your question: is this patient covered by this payer on this date, and what are the benefits? The 271 is the answer. Practice management systems and clearinghouses run these in batch (the whole schedule two days ahead) and in real time (at check-in). The quality of the 271 varies widely by payer. Some return the plan name, copay for the visit type, deductible remaining and any other coverage on file. Others return "active" and little else.
Two habits make the 271 useful. Store the response in the chart rather than just displaying it, so the member ID and demographics the payer returned can be compared with what registration typed. And read the other-coverage segment; when a 271 says another payer is on file, that is the coordination of benefits denial you are about to receive, arriving early enough to prevent.
837: the claim
The 837P is the professional claim, the electronic equivalent of the CMS-1500 form. It carries the billing provider, rendering provider, subscriber and patient, diagnoses (up to twelve), and up to fifty service lines with procedure code, modifiers, units, charge, place of service and diagnosis pointers. The 837I is the institutional version, the equivalent of the UB-04, used by facilities.
Your practice management system builds the 837 from the encounter and sends it to the clearinghouse. The clearinghouse runs its scrubber (edits for format, required fields, code validity and, if you pay for it, payer-specific rules) and either returns the claim to you as a rejection or forwards it to the payer. This is the first checkpoint, and the rejection report from the scrubber is the first report to work every morning. A claim rejected here never reached the payer and does not exist as far as the payer is concerned; the timely filing clock is still running.
999 and 277CA: the two acknowledgements
When the payer receives the 837 file, it sends back a 999. The 999 says whether the file was structurally valid. It is a syntax check, not a content check, and a rejected 999 usually means a technical problem: a malformed segment, an invalid character, a control number mismatch. When a 999 rejects, every claim in that file is rejected, and the whole batch has to be corrected and resent. This is rare with modern systems but catastrophic when it happens quietly, because a batch of 300 claims can sit rejected for weeks if nobody reads the 999s.
The 277CA is the content acknowledgement, claim by claim. For each claim in the file, it says accepted (with the payer's claim control number, which you will need for every future inquiry) or rejected (with a status code and reason). Payer front-end rejections here include provider not found or not enrolled with this payer, subscriber not found, duplicate of a claim already on file, and invalid place of service for the code. These claims, like scrubber rejections, never reached adjudication and will never appear on an 835. They only appear here.
This is the file practices neglect. The clearinghouse portal usually shows 277CA rejections under a status such as "rejected by payer," a few days after submission, mixed in with accepted claims. If nobody has a daily task to work that status, the claims age silently until someone runs an aged claims report and finds a group of 60-day-old claims with no payer response. In the RCM audits we do, unworked 277CA rejections are among the most common sources of timely filing write-offs. The fix costs nothing: a daily filter for payer-rejected claims, worked the same morning as scrubber rejections.
276/277 and 835: status and payment
The 276 is a claim status inquiry and the 277 is the response (a different use of the 277 than the 277CA, which confuses everyone). Most clearinghouses offer this as a claim status feature. It lets you ask a payer, electronically, where a claim stands, instead of calling. Many practices never turn it on and spend hours a week on hold. The response codes are standardized (finalized, paid, denied, pending, additional information requested), and a status of "not found" 30 days after a 277CA acceptance is itself a red flag worth a phone call.
The 835 is the remittance. It arrives when the payer has adjudicated the claim and either paid or denied it, and it carries the claim-level and line-level detail, the reason codes, and the provider-level adjustments. Your system matches 835 claims to your open claims by patient account number and the payer claim number from the 277CA. When the match fails (because the account number was changed, or the claim was split by the payer), the remittance lands in an unmatched queue that someone has to work. The 835 requires ERA enrollment with each payer, usually a form on the payer's site or through the clearinghouse, and a separate EFT enrollment for the money. Do both at the same time as the provider enrollment, and check that the 835s actually start arriving.
Following one claim through the files
Here is what the trail looks like for a single visit. On March 2, the batch 270 for March 4's schedule returns a 271 showing the patient active with a $30 copay and no other coverage. On March 4 the visit happens; on March 5 the 837P goes to the clearinghouse and passes the scrubber. On March 6 the payer's 999 accepts the file and on March 8 the 277CA accepts the claim with payer claim number 26066A0412. On March 24 a 276 inquiry returns "finalized, paid." On March 27 the 835 arrives with the EFT trace number, showing $92 allowed, $62 paid, $30 PR-3 copay, and a CO-45 adjustment for the rest. The system matches it to the claim by account number and payer claim number, posts it, and the patient's copay, collected on March 4, closes the balance.
When a claim is "lost," the question is which step it last appeared at. If it has no scrubber rejection and no 277CA acceptance, check the 999. If it has a 277CA acceptance but no 835 after 45 days, send a 276. If it has an 835 that did not post, look in the unmatched queue. Every step leaves a record, which is the point of the whole system.
Questions we hear
Our clearinghouse says a claim was accepted but the payer says they never got it. Who is right?
Ask which acceptance the clearinghouse means. "Accepted" often means the scrubber passed it and the file was transmitted. Payer acceptance is the 277CA. If there is no 277CA acceptance with a payer claim number, the payer is probably right, and the clearinghouse should be able to show you the 999 for that file. If there is a 277CA acceptance, give the payer their own claim control number and the conversation changes.
Do we need to read the raw files?
No. The clearinghouse and practice management system present them as reports and statuses. But you should know which report corresponds to which file, and someone in the practice should be able to open the raw 835 or 277CA when the summary screen does not explain a problem. Clearinghouses will show you the human-readable version on request.
Why do some payers still send paper remittances?
Usually because ERA enrollment was never completed for that payer, or the payer requires re-enrollment after a tax ID or bank change. Smaller payers and some workers' compensation carriers do not offer 835s at all. For any payer that does, complete the enrollment; posting paper is slower, and the reason codes are often abbreviated on paper in ways that lose information.
What to do this week
- Ask your clearinghouse for a list of every payer you bill and whether 837, 277CA, 835 and 270/271 are live for each; enroll wherever 835 is missing.
- Find the payer-rejected (277CA) status filter in your clearinghouse portal and count how many claims sit there today, by age.
- Add a daily task to work 277CA rejections alongside scrubber rejections, with one named owner.
- Turn on electronic claim status (276/277) if your clearinghouse offers it, and use it before any phone call.
- Pick one paid claim and follow it through all six files with your biller, so at least two people in the practice can trace a claim end to end.
