ACA Marketplace Plan Insurance Claim Denied? How to Appeal

If you purchased health insurance through healthcare.gov or your state's ACA marketplace and your insurer has denied a claim, you have specific rights under the Affordable Care Act that are in some ways stronger than those available to people in employer-sponsored plans. Marketplace Qualified Health Plans (QHPs) must comply with both ACA requirements and state insurance regulations, giving you two parallel avenues for challenging a denial. The ACA's Essential Health Benefits mandate means there are categories of care that QHPs simply cannot exclude — and denials in those categories are legally vulnerable.

Why ACA Marketplace Plan Claims Are Denied

Marketplace plan denials follow predictable patterns tied to the structure of QHP coverage:

• Medical necessity denials within EHB categories — Even though ACA Essential Health Benefits must be covered, insurers can still deny specific claims within those categories as "not medically necessary." These are the most common denials and are frequently overturned when the physician's documentation addresses the insurer's specific clinical criteria.
• Prior Authorization Denied: How to Appeal" class="auto-link">Prior authorization failures — QHPs require prior authorization for many services. Missing, incomplete, or untimely prior authorization requests result in administrative denials even when the underlying service is covered and medically appropriate.
• Out-of-network care denials — Marketplace plans typically have narrow networks. Care received from out-of-network providers may be denied or covered at a significantly lower rate. Emergency care protections under the ACA and the No Surprises Act (42 U.S.C. §300gg-111) limit out-of-network cost exposure for emergency situations.
• Mental health and substance use disorder parity violations — QHPs must comply with Mental Health Parity Act (MHPAEA) Explained" class="auto-link">MHPAEA (29 U.S.C. §1185a). More restrictive prior authorization, visit limits, or medical necessity criteria for behavioral health than for comparable medical services is prohibited and appealable.
• Prescription drug formulary exclusions — Marketplace plans must cover prescription drugs as an EHB, but specific drugs may be excluded from the formulary or placed on high cost-sharing tiers. Non-formulary drug denials are appealable when the drug is the medically necessary standard of care and no formulary alternative is clinically equivalent.
• Experimental or investigational treatment exclusions — Denials characterizing evidence-based treatments as experimental, particularly for cancer therapies with NCCN support or treatments with FDA approval, are legally vulnerable and frequently reversed on External Independent Review: Complete Guide" class="auto-link">external review.

How to Appeal

Step 1: Identify the ACA Legal Framework and Your Plan's EHB Coverage

Determine whether the denied service falls within an ACA Essential Health Benefit category: ambulatory services, emergency services, hospitalization, maternity and newborn care, mental health and SUD services, prescription drugs, rehabilitative and habilitative services, laboratory services, preventive care, or pediatric services. If the denied service falls within an EHB category, the plan cannot categorically exclude it — and denials must be based on a legitimate clinical ground, not a blanket exclusion. Cite the ACA's EHB mandate (42 U.S.C. §18022) in your appeal.

Step 2: Get Your Physician's Letter of Medical Necessity

The treating physician's letter is the most important document in the appeal. It must include the ICD-10 diagnosis code for the patient's condition, the CPT code for the service or procedure denied, a clinical explanation of why the denied service is medically necessary for this specific patient, and citations to relevant clinical guidelines — NCCN for cancer, AHA/ACC for cardiac care, ADA Standards of Medical Care for diabetes, APA practice guidelines for behavioral health, or USPSTF Grade A/B recommendations for preventive services. The letter should explain how the insurer's denial reason fails to account for the patient's specific clinical presentation.

Step 3: Request a Peer-to-Peer Review Within Days of the Denial

Have your physician request a peer-to-peer review with the insurer's medical director within five days of receiving the denial. ACA marketplace plan medical directors are required to be licensed physicians in the appropriate clinical specialty for the type of review conducted. Direct physician discussion citing applicable clinical guidelines resolves a significant proportion of ACA marketplace plan medical necessity denials before a formal written appeal.

Step 4: File the Internal Appeal Within 180 Days

Under ACA §2719 (42 U.S.C. §300gg-19), you have the right to an internal appeal and to independent external review for all non-grandfathered QHPs. File your internal appeal within 180 days of the denial. The plan must provide a written decision on standard internal appeals within 60 days (non-urgent) or 72 hours (urgent/expedited). Submit your appeal in writing, address every stated denial reason, and attach the physician's letter, clinical guidelines, and medical records.

Step 5: Request Independent External Review After Internal Denial

After the internal appeal is denied (or if the plan fails to decide within the required timeframe), request independent external review. For marketplace plans, the federal external review process is available through the plan. External reviewers are IROs) Explained" class="auto-link">Independent Review Organizations (IROs) staffed by board-certified physicians — their decisions are binding on the insurer. This is a particularly powerful tool for experimental treatment denials, where IROs regularly apply more current clinical standards than the insurer's own coverage policies.

Step 6: File Complaints with Your State Insurance Commissioner and HHS

For state-regulated marketplace plans, file a concurrent complaint with your state insurance commissioner as the internal appeal proceeds. The state commissioner can investigate regulatory violations including improper claim denials, failure to provide required notices, and MHPAEA violations. Contact your state insurance commissioner's office through the NAIC consumer resources at naic.org. For federal marketplace plans (healthcare.gov), contact the CMS Center for Consumer Information and Insurance Oversight (CCIIO).

What to Include in Your Appeal

• Denial letter and EOB with the specific denial reason, criteria cited, and ICD-10 and CPT codes
• Your QHP Summary of Benefits and Coverage or Evidence of Coverage showing the benefit category at issue
• Treating physician's letter of medical necessity with ICD-10 codes, CPT codes, and applicable clinical guideline citations (NCCN, AHA, ADA, APA, USPSTF)
• ACA Essential Health Benefits citation (42 U.S.C. §18022) if the denial amounts to a categorical exclusion within an EHB category
• MHPAEA citation (29 U.S.C. §1185a) for mental health, substance use disorder, or behavioral health denials

Fight Back With ClaimBack

ACA marketplace plan denials in Essential Health Benefit categories are among the most legally vulnerable insurance denials — insurers cannot categorically exclude covered EHB services, and external reviewers apply current clinical standards rather than outdated insurer coverage policies. A well-structured appeal citing the ACA's EHB mandate, applicable clinical guidelines, and the specific denial grounds gives you real leverage at every stage. ClaimBack generates a professional appeal letter in 3 minutes.

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Related Reading

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