Read the denial, win the appeal

More than 80% of appealed Medicare Advantage (MA) prior authorization (PA) denials are overturned. Most practices never appeal. The denial code tells you exactly why you were denied and exactly what to send back.

When a Medicare Advantage (MA) plan denies a prior authorization (PA) request and a provider appeals, the plan reverses the denial more than 80% of the time. In 2024, 80.7% of appealed MA PA denials were fully or partially overturned. In 2023 the figure was 81.7%. These numbers come from KFF's May 2025 analysis of the nearly 53 million PA determinations MA insurers made in 2024. The payers are not winning these on appeal. Practices just are not showing up.

Fewer than 1% of denied ACA (Affordable Care Act) marketplace claims were internally appealed in 2024, per KFF's analysis of CMS (Centers for Medicare and Medicaid Services) transparency data. The math: a denial that takes 20 minutes to appeal has a greater than 80% chance of reversal in MA. Most practices absorb the loss instead, because no one has time, or because the denial code looks inscrutable, or because the billing coordinator has 40 other things open. The money sits on the table.

The denial code is actually readable once you know the key. A CO-97 remark code on an explanation of benefits (EOB) means the payment was bundled into another service billed on the same date. A CO-197 means the claim went out without a prior authorization number attached. Both are fixable without a clinical argument. In September 2024, a nine-clinician outpatient behavioral health group in Fort Collins, Colorado received CO-197 denials on 23 partial hospitalization program (PHP) level-of-care claims from a commercial payer. The billing director, working from her practice management system, pulled the PA approvals, confirmed each one had been obtained before the service date, and filed appeals with the authorization numbers attached. All 23 reversed within 45 days. The practice recovered $52,000. The PAs had been approved; they just never made it onto the original claim. One missing field, 45 days, $52,000 back.

For denials that do hinge on medical necessity, the Mental Health Parity and Addiction Equity Act (MHPAEA), the 2008 federal law requiring insurers to cover behavioral health at parity with medical and surgical benefits, gives the appeal more weight than most billing staff realize. If a payer applies stricter level-of-care criteria to behavioral health PHP or intensive outpatient program (IOP) claims than it applies to comparable medical or surgical admissions, that is a non-quantitative treatment limitation (NQTL) disparity and a potential MHPAEA violation. The Department of Labor (DOL) FY 2023 MHPAEA enforcement findings describe exactly this pattern across multiple plans. Citing it in an appeal letter, with a specific comparative example, shifts the burden to the payer to justify the discrepancy.

For coverage denials that reach external independent review, also called independent review organization (IRO) review, the picture gets even better. A Health Affairs study of 51,394 external review cases in New York state from 2019 to 2025 found that 46.7% were overturned at that third level. For behavioral health claims specifically, IRO overturn rates ranged from 57% to 82%.

So here is the move for the clinic owner in Fort Collins, or anywhere else carrying a denial backlog: pull every open denial from the last 120 days, sort by CO or PR remark code, and work the CO-197s first. Those are the ones where you already won the clinical argument and a missing field is the only thing between you and payment. Set a calendar reminder for 60 days out on each one, because payer appeal windows close and they do not reopen. The CO-97s and medical necessity denials come next, with MHPAEA language ready for anything behavioral health. None of this requires a lawyer. It requires the right document attached to the right code, filed before the deadline.