Top 10 claim denials in medical billing (and how to prevent each one)
Most denial workflows are built to fight claims after they're rejected, but the highest-return work in the revenue cycle happens earlier: Preventing denials before they start. This guide breaks down the ten most common types of denials and shows you how to deploy prevention strategies to stop revenue loss at the source.
Denial prevention strategies to curb $43 billion in hospital payment recovery costs
In 2025, U.S. hospitals spent more than $43 billion trying to collect payments for care they had already delivered, according to the American Hospital Association. That is the price of chasing money you already earned, and it keeps rising as denials are increasing across nearly every payer.
A large share of those denials is administrative and avoidable.
When the root cause is a missing authorization or an eligibility error, the fix belongs upstream, at registration and pre-bill review rather than in an appeal queue months later.
Denials driven by front-end and process errors are winnable when you move resources toward preventing them instead of reworking them. The ten categories below are where that shift pays off fastest.
1. Prior authorization failures
What it is: These denials hit when a service required prior authorization, and that approval was either missing or didn't match the procedure performed.
Why it happens: Most trace back to a simple sequencing problem. The authorization was never secured before the service, or the payer approved one CPT while the clinician performed another. Approvals that lapse before the date of service create the same result.
How to prevent it: Confirm the authorization covers the exact CPT you plan to bill and is still active on the date of service.
Re-check any time the procedure or the plan changes after the initial sign-off. A payer-specific requirement matrix helps schedulers flag which services need authorization for which plans before anything gets booked.
These denials are also among the most recoverable, so the ones that slip through are worth pursuing.
KFF found that only 11.5% of denied Medicare Advantage prior-authorization requests were appealed in 2024, and 80.7% of those appeals succeeded.
2. Patient eligibility and coverage issues
What it is: The patient's coverage was inactive on the date of service, or the plan details on the claim didn't match the payer's records.
Why it happens: Eligibility gets checked once at scheduling and never confirmed again, so a coverage change before the visit goes unnoticed. Simple transcription errors in the member ID or date of birth produce the same rejection.
How to prevent it: Run real-time eligibility at scheduling and again at check-in, and verify plan-specific benefits rather than a simple active or inactive status.
Confirm the member ID and date of birth against the card at registration so a typo never reaches the payer. Re-verify whenever coverage could have shifted, such as a new plan year or a job change, since those transitions are where stale eligibility data does the most damage.
3. Medical necessity denials
What it is: The payer agrees that the service happened but decides that the documentation didn't justify it as medically necessary for the diagnosis submitted.
Why it happens: The clinical documentation doesn't meet the criteria in the payer's Local Coverage Determination (LCD), National Coverage Determination (NCD), or medical policy. Even when the service was appropriate, the record may not demonstrate the diagnosis, severity, or failed conservative treatment the payer requires to consider it medically necessary.
How to prevent it: Check the payer's medical policy and the applicable LCD or NCD before delivering any scheduled service, and code to the full ICD-10 specificity that supports necessity.
Build concurrent clinical documentation review into the encounter so gaps get closed while the patient is still in-house, when documentation is easiest to correct. For traditional/fee-for-service Medicare claims likely to fail a necessity test, issue an ABN so the balance stays billable to the patient.
Medical necessity denials are among the most contested, and payers reverse a large share of them on appeal. One Health Affairs analysis found Medicare Advantage plans denied roughly 17% of claims, with 57% ultimately overturned.
Prevention keeps those cases out of the appeal queue in the first place.
4. Incomplete or insufficient clinical documentation
What it is: This denial comes when the medical record doesn't fully support the services or diagnoses on the claim.
Why it happens: Documentation is written for clinical care first, so the billing-critical details often go missing. A note may lack the specificity a code requires, or it may arrive unsigned or too late to support timely billing.
How to prevent it: Give clinicians documentation templates tied to your highest-risk diagnoses so the required elements get captured the first time. Showing physicians exactly how their wording affects reimbursement and audit exposure is one of the most effective ways to close gaps before they turn into denials.
Move clinical documentation integrity upstream by querying physicians during the encounter, while the care is fresh and the record can still be corrected.
5. Coding errors (ICD-10, CPT, HCPCS)
What it is: Codes that are outdated or that don't match the documentation and the other codes on the claim.
Why it happens: A diagnosis code lacks specificity, or a code set changes and the old value keeps getting applied. CMS revises ICD-10 every fiscal year, so last year's correct code can quietly become this year's denial.
How to prevent it: Run automated coding edits before the claim drops and code to the highest specificity the record supports.
Schedule annual coder and CDI training on the IPPS final rule and the yearly ICD-10 and CPT updates so changes get caught at the source.
Regular coding audits against national benchmarks surface the patterns worth fixing before a payer finds them.
6. Non-covered or excluded services
What it is: The service isn't a covered benefit under the patient's specific plan.
Why it happens: Usually a benefit exclusion or a plan limit, such as a capped number of visits per year or a service the plan treats as experimental. Coverage also varies widely by payer program, so a service covered under one plan can be excluded under another.
How to prevent it: Verify covered benefits and any coverage limits before the service, and capture patient liability with an ABN or advance notice of non-coverage when a service falls outside the plan.
Flag plan-specific exclusions during scheduling so patients can weigh financial responsibility ahead of time.
Payer-specific programs carry their own coverage rules, and understanding why VA hospital claims are rejected helps teams anticipate exclusions that standard commercial logic would miss.
7. Timely filing and late submission
What it is: The claim simply arrived after the payer's filing deadline. This is one of the most preventable types of denials.
Why it happens: Deadlines vary widely, from 90 days to a full year, and each payer counts from its own starting point. A clean claim that stalls in internal review or bounces back for a minor error can burn through the window before anyone notices.
How to prevent it: Track each payer's filing clock from the date of service and set automated aging alerts well before the deadline.
Prioritize first-pass claim accuracy so rework doesn't eat the remaining days.
For any claim that stalls internally, build an escalation trigger that surfaces it while there is still time to file.
8. Coordination of benefits (COB) errors
What it is: The payer believes another insurer should have paid first, or the primary and secondary order on the claim is wrong.
Why it happens: Patients with more than one active plan are the usual trigger. When the payment order is unclear or the primary payer's information is missing, the secondary payer rejects the claim until the sequence gets resolved.
How to prevent it: Confirm the primary and secondary payer order at registration and re-verify it any time coverage changes.
Attach the primary payer's EOB to the secondary claim so the payment sequence is documented on submission. Some payers have also begun requiring proof that the primary was billed within its filing limit, so fold that documentation into your secondary-claim workflow.
9. Bundling and unbundling errors
What it is: These denials come from how procedure codes are combined, either bundling services that should be billed together or unbundling ones that shouldn't be split.
Why it happens: Most are caught by the National Correct Coding Initiative (NCCI) edits, which compare code pairs billed for the same patient on the same day and deny one of them when the pairing breaks the rules. NCCI edits apply to professional claims, while facility and outpatient hospital claims are governed by the Outpatient Code Editor (OCE). Improper unbundling commonly triggers a CO-97 denial and can invite a payer audit.
How to prevent it: Apply NCCI edits before the claim goes out and use modifiers only when the documentation clearly supports separate billing.
Audit your highest-volume code pairs regularly, so recurring errors get corrected at the template level.
When a modifier is in question, confirm the record justifies it before submission.
10. Payer policy changes and AI-driven algorithmic denials
What it is: Payers update coverage rules or run claims through automated algorithms that reject them in seconds.
Why it happens: Payers increasingly use AI to review claims at a speed and scale no manual team can match. A Stanford-led review in Health Affairs described the dynamic as an "arms race," and an NAIC survey of 93 large insurers found 84% already use AI in their operations. Automated denials often apply rigid criteria without weighing a patient's clinical circumstances.
How to prevent it: Monitor payer policy bulletins and track denial patterns by payer and denial type so you can spot algorithmic behavior early.
When a denial originates from an algorithm rather than a clinical reviewer, frame the appeal around the criteria the system overlooked. Denial patterns also vary sharply by payer. Understanding why Medicaid MCO denials exceed Medicare Advantage helps teams direct effort where the risk runs highest.
Note: Under CMS-4208-F, effective January 1, 2026, once a Medicare Advantage plan approves an inpatient admission it generally cannot reverse that approval based on information gathered afterward. Teams unaware of this protection may concede reversals they no longer have to accept.
How EnableComp can help
EnableComp's denial management suite pairs specialized analytics with clinical and billing expertise to resolve complex denials that slip through standard revenue cycle workflows.
Instead of working every denial the same way, EnableComp uses systematic detection logic to surface high-risk claims and root-cause patterns at scale, paired with a prevention workflow built around payer-specific rules and timely filing requirements.
Schedule a consultation to see how much revenue you're leaving behind.
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About the author
Kelsey Taylor, BSN, RN, is the Senior Director of Clinical Denials at EnableComp, bringing over 10 years of experience in healthcare management and clinical operations to the role. Her background spans clinical quality, care management, and product management, giving her a well-rounded lens on how revenue cycle, training, and clinical operations intersect. She’s passionate about empowering teams to deliver patient-centered, impactful results and frequently speaks on topics like DRG revenue integrity, complex revenue recovery, and denial prevention strategy.













