The denial letter from your health insurance company arrived with language that felt final. “This service is not medically necessary.” “Prior authorization was not obtained.” “This service is not covered under your plan.” None of these sentences mean you have no options. They mean you have received the first word — not the last.
Across ACA marketplace plans, UnitedHealthcare denied approximately 20% of claims in the 2024 plan year. For Medicare Advantage prior authorisations, denial rates run as high as 12.8% at major carriers. And in each of these categories, 80%+ of properly filed appeals are overturned. The gap between how many people could win an appeal and how many actually file one is the single most fixable gap in American healthcare access.
Step 1: Read the Denial Letter and Identify the Denial Type
Before anything else: read the Explanation of Benefits (EOB) or denial letter carefully. The denial type determines your strategy. Most denials fall into one of five categories:
| Denial Type | What It Means | Your Angle |
|---|---|---|
| Medical necessity | Insurer claims service is not clinically required | Physician letter + peer-reviewed literature showing it is |
| Prior authorization | Approval was not obtained before service | Retroactive PA request; argue provider did not know it was required |
| Coding error | Wrong CPT or ICD-10 code submitted | Request corrected claim with provider; resubmit |
| Out-of-network | Provider not in plan network | Continuity of care or No Surprises Act protections may apply |
| Coverage exclusion | Benefit is not part of your plan at all | Harder to appeal; check if exclusion applies correctly; state protections may override |
Under the 2026 CMS Interoperability and Prior Authorization Final Rule, insurers must provide a specific clinical reason for every denial. If your letter does not clearly explain the clinical basis, call the insurer and ask for the specific clinical policy number they applied. You are entitled to this information, and the specific language they give you becomes the foundation of your appeal.
Know Your Deadlines — They Are Not Negotiable
Every appeal has a window. Missing it is one of the few reasons an otherwise winnable case cannot be pursued. Key deadlines to know:
- Internal appeal: Most plans require you to file within 180 days of receiving the denial (commercial plans). Medicare Advantage gives you 60 days. Check your plan documents — some carriers use a 60- or 90-day window even for commercial plans.
- External review: After exhausting internal appeals, you typically have 4 months to request an external independent review.
- Expedited review: If your health is at immediate risk, you can request an expedited internal appeal — the insurer must respond within 72 hours. Your physician can certify the urgency.
- Urgent prior authorization: For ongoing treatment that is time-sensitive, request an expedited PA determination. Insurers must respond within 72 hours under 2026 CMS rules.
Step 2: Build Your Appeal File
The quality of your documentation is the primary driver of appeal outcomes. A letter that simply says “I disagree with this decision” will almost certainly be upheld. An appeal that responds specifically to the stated denial reason with counter-evidence succeeds the majority of the time. Build your file before you write a single word of the appeal letter.
Your appeal file should include:
- The denial letter with the specific clinical reason highlighted
- Your physician’s letter of medical necessity — signed, addressing the exact denial reason, explaining why this specific treatment is clinically necessary for your individual health situation. This is the most important document in any appeal.
- Relevant clinical records — office notes, specialist reports, lab results, imaging reports from the past 12 months that support the medical necessity argument
- Peer-reviewed medical literature — published studies or clinical guidelines that support the treatment being standard of care for your condition
- The insurer’s own clinical guidelines — most insurers publish their medical necessity criteria online. If your situation meets their own stated criteria, quote those criteria directly in your appeal
CMS rules require that medical necessity determinations be made based on “the circumstances of each individual patient,” not population-level statistical averages. If the insurer’s denial is based on a general policy (“this procedure is not typically required for patients with your diagnosis”), your physician’s letter should explicitly explain how your case departs from the typical presentation and why that departure makes the treatment necessary specifically for you.
Step 3: Write Your Appeal Letter
The appeal letter has a specific structure that works. Follow it:
- Opening — state what you are appealing and when: “I am filing a first-level internal appeal of the denial issued on [date] for [service/procedure], under claim number [XXXXX].”
- Quote the denial reason: “The denial letter states the service was denied because [exact language from letter].”
- Counter the denial reason directly: “This determination is incorrect for the following clinical reasons: [your physician’s specific argument].”
- Cite your evidence: Reference each document in your file. “As documented in my treating physician’s letter (Attachment A) and supported by [clinical guideline] (Attachment B)…”
- State the outcome you are requesting: “I request that this denial be reversed and the claim be approved and processed.”
- Include your contact information and a response deadline reminder: Reference the plan’s obligation to respond within the required timeframe.
Step 4: External Independent Review — Your Most Powerful Tool
If your internal appeal is denied, your right to external review is one of the most underused consumer protections in American health insurance law. Under the ACA, you have the right to have your case reviewed by an Independent Review Organisation (IRO) — a third-party medical review body with no financial relationship with your insurer.
The external reviewer is a clinician, not an administrator. They evaluate your case on its medical merits. This is where the 80%+ overturn rate in Medicare Advantage cases largely originates — independent clinical reviewers looking at the actual evidence reach the conclusion that the care was medically necessary far more often than the algorithm or insurer’s internal reviewer did.
To request external review, contact your state insurance department or follow the instructions in your internal appeal denial letter. Federal law requires that external review decisions for medical necessity denials be binding on the insurer.
When Appeals Do Not Resolve It: Other Paths
State insurance commissioner complaint. Filing a complaint with your state’s insurance regulatory agency puts your insurer on notice that a regulator is watching the case. Insurers sometimes reverse denials quickly once a regulatory complaint is filed. Find your state commissioner at naic.org.
Provider advocacy. For complex cases involving expensive procedures, your provider’s billing department often has experienced staff who manage appeals as part of their routine work. Ask your provider’s office to file a parallel appeal on their side — providers have more leverage with insurers than individual patients because of the ongoing financial relationship.
Patient advocates. Professional patient advocates (some free through hospitals, some fee-based) specialise in insurance appeals and can manage the process if you are dealing with a complex or high-stakes denial during a difficult illness.
