7 Most Common Claim Denial Reasons & How to Fix Each

Denials feel random when you're staring at a worklist of hundreds. They're not. The vast majority fall into seven categories, each with a standard fix. Learn the pattern once and every denial becomes a routing decision instead of a research project.

CO-16

1. Missing or invalid information

The claim lacks data the payer needs to adjudicate it — wrong member ID, missing NPI, invalid diagnosis code, blank required fields, or a diagnosis that doesn't support the procedure billed.

The fix: read the remark code for exactly what's missing, correct it, and resubmit as a corrected claim (not a duplicate). Prevention: a claim scrubber validates member IDs, NPIs, diagnosis pointers, and required fields before submission — this entire category is largely preventable.

Eligibility

2. Patient not eligible / coverage terminated

The patient wasn't covered on the date of service — lapsed policy, wrong payer billed, or coordination-of-benefits issues where another payer is primary.

The fix: verify eligibility for the exact date of service. If coverage was active, appeal with proof (eligibility response, payer portal screenshot). If another payer is primary, bill them first. Prevention: verify eligibility and benefits at every visit — not just the first one.

CO-197

3. No prior authorization

The service required prior authorization and none was on file. This is one of the fastest-growing denial categories as payers expand auth requirements.

The fix: if an auth exists, appeal with the authorization number. If not, request a retro-authorization, documenting any clinical urgency. Our prior auth appeal letter guide covers the clinical case. Prevention: check auth requirements before the date of service, every time.

CO-96

4. Non-covered charges / not medically necessary

The payer says the service isn't covered under the patient's benefit plan, or wasn't medically necessary as documented.

The fix: this is a documentation fight. Appeal with chart notes, test results, and clinical guidelines supporting medical necessity. If it's a true benefit exclusion, check for secondary coverage before writing it off. Prevention: verify benefits for high-dollar services up front and get Advance Beneficiary Notices signed where appropriate.

CO-97

5. Bundled into another payment

The payer considers the charge included in another procedure's allowance (NCCI procedure-to-procedure edits). Common with E/M visits billed alongside procedures.

The fix: if the services were truly separate and distinct, append the appropriate modifier (25, 59, or an X-modifier like XE/XP/XS/XU) with documentation supporting it, and appeal. If the edit is correct, the denial stands — adjust your coding. Prevention: run NCCI edit checks in your scrubber before billing.

Coding

6. Incorrect coding — CPT, ICD-10, or modifiers

Wrong diagnosis code, CPT that doesn't match the documentation, missing modifiers, or code pairs that trigger payer edits.

The fix: correct the coding to match the documentation and resubmit as a corrected claim. Never change codes to chase payment — code what the documentation supports. Prevention: coding review on high-dollar claims and regular coder education on payer-specific rules.

CO-29

7. Timely filing expired

The claim arrived after the payer's filing deadline. Unlike the other six, this one is usually unfixable — and unbillable to the patient.

The fix: appeal only with proof of timely submission (clearinghouse acceptance reports, 277CA acknowledgments). Without proof, the revenue is lost. Prevention: track every claim against per-payer deadlines — see our timely filing limits guide. This is the denial category where prevention is everything.

Turning patterns into prevention

Once you classify denials, the data tells you where to invest. If CO-16 dominates, fix your front-end data capture and scrubbing. If CO-197 dominates, fix your auth workflow. If CO-97 dominates, educate your coders. Track denial reason codes monthly, and attack the top two categories — that's where the recovered revenue lives. And when a denial does land, work it fast: our step-by-step appeal guide covers deadlines, letters, and follow-up.

How to read a denial on the remittance advice

Every denial on an 835 remittance file arrives as a code pair. Learning to read them is the core skill of denial management:

CARC (Claim Adjustment Reason Code): the broad category — why the payer adjusted the claim. CO-16 (missing information), CO-96 (non-covered), CO-97 (bundled), CO-29 (timely filing). The "CO" prefix means Contractual Obligation — the provider absorbs it and generally cannot bill the patient.
RARC (Remittance Advice Remark Code): the detail — what specifically the payer wants. A CO-16 with remark code N390 ("missing/incomplete/invalid patient birth date") tells you exactly what to fix.
Group codes matter: CO (contractual obligation) means you absorb it; PR (patient responsibility) means it can go to patient statements; OA (other adjustments) is payer-specific. Misreading the group code is how practices accidentally bill patients for contractual adjustments — a compliance risk.

Build a reference sheet of your top 20 CARC/RARC combinations with the standard fix for each. New billers become productive in days instead of months when the playbook already exists.

Measure, then attack

You can't fix what you don't measure. Every month, pull two reports: denial rate by reason code (which categories dominate?) and denial rate by payer (is one payer an outlier?). The intersection is your project list — "CO-197 denials from Payer X" is a solvable problem with an owner and a deadline; "denials are up" is not. Re-run the reports monthly and watch the top categories shrink as your fixes take hold.

Illustration of denial reason analysis by category

Denial categories behind most lost revenue — each with a specific fix. Categorize first, then act.

Frequently asked questions

What is the most common reason claims are denied?

Missing or invalid information (CARC CO-16) is consistently among the top denial reasons — wrong member IDs, missing NPIs, invalid diagnosis codes, or incomplete claim data. It is also the most preventable: claim scrubbing before submission catches the majority of these errors.

What does denial code CO-97 mean?

CO-97 means the payer considers the service bundled into another payment already made — the charge is included in a different procedure's allowance. Check NCCI procedure-to-procedure edits and whether a modifier (such as 25, 59, or an X-modifier) correctly describes a separately payable service.

Can you fix a claim denied for no authorization?

Often yes. If an authorization exists but wasn't on the claim, appeal with the auth number. If none was obtained, request a retro-authorization from the payer, documenting any clinical urgency. If neither is possible, the denial usually stands — which is why front-end auth verification matters.

How do I reduce claim denials overall?

Scrub claims before submission, verify eligibility and benefits on every visit, confirm authorizations before the date of service, track denial reason codes to find your top patterns, and work denials within days — not weeks — so appeal deadlines never lapse.