Claim Rejections vs Denials (Clearinghouse and EDI Errors)

How to Read 999 and 277CA Reports, Fix the Common Errors and Protect Your Filing Deadline

By Team Rcmaxis  ·  October 15, 2026  ·  11 min read

A claim that gets rejected at the front end never reaches the payer's adjudication system, never produces a remittance and never gets paid. If nobody reads the reject report, nobody knows it happened. A 99214 pays $135.61 under 2026 Medicare rates, so 30 unworked rejections a month is $4,068 a month, or $48,816 a year (30 x $135.61 x 12). That's before the filing clock runs out and the claim becomes unrecoverable.

Rejections are the cheapest problem in billing to fix and the easiest to lose track of. They don't show up on a denial report, because there's no denial. They show up on an acknowledgement report that most practices skim at best.

Here's how a rejection differs from a denial, how to read the 999 and 277CA reports, the errors that cause most rejections, and why a rejected Medicare claim never stops your timely filing deadline.

Claim Rejections vs Denials: What's the Difference?

A rejection means the claim failed a front-end edit and was never accepted for processing. A denial means the payer adjudicated the claim and decided not to pay it, in whole or in part. Treating one like the other wastes time, and with Medicare it can cost you the claim.

Medicare's own manual defines the terms. An unprocessable claim is any claim with incomplete or missing required information, or complete information that's invalid. The manual's examples are a missing NPI (incomplete) and an expired or incorrect NPI (invalid). When the problem is caught at the front end, the claim is returned to the provider, the claim data isn't kept in the system and no remittance advice is issued.

How to Read 999 and 277CA Reports

Two acknowledgements tell you what happened to a claim file, and they answer different questions. Read both, every day.

The 999 is the file-level check. It tells you whether the transmission's structure was accepted, accepted with errors or rejected. If the whole file is rejected, none of the claims in it get processed. The 999 can't tell you anything about an individual claim's content.

The 277CA is the claim-level check. It reports, claim by claim, whether the claim passed the payer's pre-adjudication edits. Its status category codes are the part to learn.

A clean 999 doesn't mean your claims were accepted. It only means the file was readable. The claims can still reject one by one on the 277CA.

The Medicare contractors publish their own 999 and 277CA response guidance, including the CGS 277CA tool listed in the references. Our update on the October 2026 Medicare EDI front-end edits covers the latest edit changes that can send claims to this queue.

Top Clearinghouse Rejection Reasons and How to Fix Them

Most rejections trace back to registration and setup, not to coding. That's good news, because those causes repeat, and you can fix them once.

The diagnosis row is worth planning for every year. New and deleted codes take effect on October 1, and a scrubber that isn't updated on time will reject claims that used to pass. Update your pick lists and edits before that date.

Medicare Unprocessable Claims: CARC 16, MA130 and No Appeal Rights

When Medicare returns a claim as unprocessable, you'll often see it described as CARC 16 with remark code MA130. The remark code says the claim contains incomplete or invalid information and that no appeal rights apply because the claim is unprocessable.

CARC 16 is a broad code. It never tells you what to fix by itself, so read the remark code that comes with it. The remark code names the specific problem, and the rest of this process follows: find the data element, correct it and send a new claim. Our guide to CARC and RARC denial codes walks through reading a remittance line by line.

Medicare contractors also point out that resubmitting an unprocessable claim won't trigger a duplicate denial, as long as that service for the same beneficiary and date wasn't previously paid. Send the corrected claim as a new claim, not as a correction to a claim that never processed.

Timely Filing: Why a Rejection Doesn't Stop the Clock

Medicare requires claims to be filed within 12 months, or one calendar year, after the date of service (42 CFR 424.44). For professional claims the line item "From" date starts the clock. For institutional claims with span dates, the "Through" date does.

A claim returned or rejected as unprocessable isn't considered filed. That means the 12 months keep running while it sits in your reject queue. A 99214 that ages past the deadline is $135.61 gone for good, and it won't appear on any denial report because it never got far enough to be denied.

Commercial payers set their own limits in their contracts, and those windows are often much shorter than Medicare's. Look them up, put them in your billing system and sort your reject queue by the date the filing window closes.

Build a Daily Rejection Workflow That Protects Revenue

The practices that don't lose claims to rejections all do the same boring thing: someone reads the acknowledgement reports every day and fixes what they find.

Take a billing team that works 30 rejected claims a month and spends 10 minutes on each. That's five hours of work protecting $4,068 a month in Medicare 99214 payments alone. The math only gets better when a root-cause fix removes a whole category of rejection.

• Morning: pull the 999 and 277CA reports, and flag any file-level rejection first, because it holds every claim in the file.
• Same day: correct and resubmit claim-level rejections, noting the reason code in the claim notes.
• Weekly: review rejections by reason and payer, and send fixes upstream to registration, scheduling or the charge master.
• Monthly: compare accepted claims to claims submitted, so a missing claim shows up before the deadline does.

Track the share of claims accepted on first submission and the time from rejection to resubmission. Our guide to medical billing KPIs shows how to build those into your dashboard, and our denial management strategies cover what to do once a claim passes the front end and comes back denied.

Audit and Compliance Exposure on Resubmitted Claims

Rejected claims aren't audited, because they never entered the system. What you do to clear them is another matter. The risks sit in the fix, not in the rejection.

The common mistakes are changing a diagnosis or code only to get past an edit, rather than because the record supports the change, and resubmitting a claim that had already adjudicated. Medicare's manual treats exact and suspect duplicates as a separate edit category, so a careless resend can produce a duplicate denial or an overpayment.

Medicare contractors can reopen a claim within one year for any reason and within four years for good cause (42 CFR 405.980). Recovery auditors generally look back three years. If a review finds that a claim was changed without support in the record, the repayment can reach back through that whole window, and the 60-day overpayment rule starts counting from the day you identify the problem. Our guide to RAC audits explains what reviewers pull, and our article on the 60-day overpayment rule covers what to do when you find one.

Frequently Asked Questions About Claim Rejections

What is the difference between a claim rejection and a claim denial?

A rejection happens before the payer adjudicates the claim. The claim fails a front-end edit, never enters the payer's adjudication system and never gets a remittance, so you fix it and send it again. A denial happens after adjudication and shows up on the remittance with a CARC and often a RARC, so you correct it through a reopening or an appeal.

Can you appeal a rejected claim?

Not for Medicare. A claim returned as unprocessable has no initial determination, so there are no appeal rights. Correct the error and submit a new claim. Medicare contractors warn that appealing an unprocessable claim only delays payment and can lead to a timely filing denial if the corrected claim isn't filed in time.

Does a rejected claim count toward the timely filing limit?

For Medicare, no. A claim returned or rejected as unprocessable isn't considered filed, so the 12-month clock from the date of service keeps running. Correct and resubmit within that window. Commercial payers set their own limits, which are often much shorter, so check each contract.

What is the difference between a 999 and a 277CA?

The 999 tells you whether the file's syntax was accepted, accepted with errors or rejected. The 277CA reports claim by claim whether each claim passed the payer's pre-adjudication edits and was accepted into adjudication. A clean 999 doesn't mean your claims were accepted, so read the 277CA too.