The insurance industry benefits enormously from the gap between what policyholders are entitled to and what they actually claim. KFF analysis of ACA marketplace data confirms that appeal rates remain extremely low despite meaningful overturn rates. Across every major insurance market, data consistently shows that a substantial proportion of denied claims are overturned on appeal — yet the vast majority of denied claimants never file one. Understanding the data — and what drives successful appeals — can change that.

Why Insurers Deny Claims

Medical necessity disputes. The insurer's internal reviewer disagreed with your treating physician's assessment. This is the most common and most commonly overturned denial type on appeal.

Prior Authorization Denied: How to Appeal" class="auto-link">Prior authorization failures. Pre-approval was not obtained or was insufficient. Many of these are reversed when proper documentation is submitted with the appeal.

Coding and billing errors. Incorrect CPT or ICD-10 codes — among the easiest denials to reverse through simple administrative corrections.

Experimental or investigational classification. External Independent Review: Complete Guide" class="auto-link">External reviewers frequently overturn these when the treatment is supported by clinical guidelines from NCCN, AAN, AHA/ACC, or ASCO.

Out-of-network provider use. Under the No Surprises Act (Public Law 116-260), many such denials for emergency services are now prohibited.

erisa-employer-plans-shows-that-consumers-win-70-of-external-reviews-for-aca-marketplace-plans-independent-external-reviews-also-see-significant-reversal-rates---internal-appeal-success-internal-appeals-succeed-less-often-than-external-reviews-but-even-here-a-meaningful-percentage-of-decisions-are-reversed--often-because-the-internal-appeals-team-applies-more-scrutiny-to-borderline-denials"><<<<<<< HEAD - External review success rate: US government data on ERISA employer plans shows that consumers win 70% of external reviews. For ACA marketplace plans, independent external reviews also see significant reversal rates. - Internal appeal success: Internal appeals succeed less often than external reviews, but even here, a meaningful percentage of decisions are reversed — often because the internal appeals team applies more scrutiny to borderline denials.

How to Appeal

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Step 1: File an Internal Appeal Within 180 Days

Under ERISA 29 CFR § 2560.503-1 and ACA 45 CFR § 147.136, you have 180 days from the denial notice to file an internal appeal for most commercial plans. Submit a written appeal letter that addresses the specific denial reason, includes a physician support letter, and cites relevant clinical guidelines from specialty societies.

Step 2: Request Peer-to-Peer Review

Ask your doctor to speak directly with the insurer's medical reviewer. This resolves many medical necessity denials without further escalation and is especially effective when the insurer's reviewer lacks specialty expertise.

Step 3: Request External Review if Internal Appeal Fails

File for external review within 4 months of the final internal denial under ACA 45 CFR § 147.136(d). The external reviewer is an independent physician with no financial ties to the insurer. California's DMHC has published data showing Independent Medical Review overturn rates consistently above 60% in recent years. Standard external review decisions are required within 45 days; expedited within 72 hours.

Step 4: File a State Insurance Department Complaint

File with your state insurance commissioner to create a regulatory record and prompt investigation. Regulatory pressure often produces results even while external review is pending.

Step 5: Request Expedited Review if Medically Urgent

If your situation is urgent, invoke expedited review under 45 CFR § 147.136. The insurer must respond to expedited internal appeals within 72 hours, and expedited external review within 72 hours as well.

Step 6: Consider Legal Action if All Administrative Remedies Fail

For high-value claims where external review and regulatory complaints have not resolved the denial, consult an ERISA attorney about federal court review under ERISA § 502(a)(1)(B). Many ERISA attorneys work on contingency given the attorney fee provision in ERISA § 502(g).

What to Include in Your Appeal

• Denial letter with the specific reason cited
• Treating physician's letter directly addressing the denial criteria with ICD-10 codes
• Medical records (lab results, imaging, specialist reports, treatment history)
• Published clinical guidelines from relevant medical societies (NCCN, AHA, APA, ASAM)
• Peer-reviewed literature for experimental or investigational denial types
• Proof of submission with timestamps

Fight Back With ClaimBack

The numbers do not lie: appeals work, and most people who could win one never try. A well-prepared appeal that directly addresses the denial reason and cites the correct clinical guidelines and federal statutes dramatically increases your odds. ClaimBack generates a professional appeal letter that gives your case the strongest possible chance of success — in 3 minutes. Start your free claim analysis → Free analysis · No credit card required · Takes 3 minutes

Related Reading

• How to Write an Insurance Appeal Letter
• What Is Medical Necessity?
• Internal vs External Insurance Appeal