The 5 Most Common Reasons Insurers Deny Claims
Each requires a different strategy. Your appeal letter should address the specific reason, not just say "I disagree."
1. Prior Authorization Not Obtained
The insurer says you should have gotten pre-approval before receiving the service. Strategy: appeal with a letter from your doctor stating the care was urgent or emergent.
2. Out-of-Network Provider
You saw a provider who doesn't participate in your plan. Strategy: check if you were referred or if the in-network alternatives were inadequate; some states have "any willing provider" rules.
3. Not Medically Necessary
The insurer's medical reviewer decided the treatment was not required. Strategy: your doctor's clinical notes and peer-reviewed guidelines supporting the treatment are your strongest evidence.
4. Experimental or Investigational
The treatment is considered unproven or not yet accepted as standard care. Strategy: cite clinical trial data, FDA approvals for the treatment's use, and NCCN or similar guideline endorsements.
5. Coding Errors / Billing Mistakes
The provider submitted the wrong CPT or ICD-10 code, causing a mismatch with your plan's coverage. Strategy: request an itemized bill, identify the incorrect code, and ask your provider to resubmit with the correct code.
The 4 Levels of the Appeals Process
| Level | Who Reviews It | Typical Deadline | Best For |
|---|---|---|---|
| 1. Internal Appeal | Your insurance company — a different reviewer than the one who denied the claim | 180 days (ERISA) / 60 days (individual/marketplace) | Any denial — start here every time |
| 2. External Review | Independent third-party reviewer (state regulator or federal ERO) | 4–6 weeks for decision after filing | Medical necessity denials; high-value claims |
| 3. ERISA Arbitration / Federal Court | Plan administrator → federal district court | Varies — no strict deadline but file promptly | Large dollar amounts; ERISA plan violations |
| 4. State Insurance Department | Your state's insurance commissioner | Varies by state | Marketplace plan issues; bad-faith insurer behavior |
How to File Your Appeal: Step by Step
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Read the denial notice carefully
The notice contains the denial reason code, the specific plan provision being applied, and the exact deadline to appeal. Don't skip this — it tells you exactly what you need to argue against. Circle the reason code and note which part of your plan it's citing.
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Gather your medical records and supporting documentation
Request your doctor's clinical notes, test results, imaging reports, and any peer-reviewed literature supporting the treatment. A letter from your treating physician explaining why the care was medically necessary is worth its weight in gold. Get these records as fast as possible — you can often submit additional information during the review.
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Write the appeal letter
Address each point in the insurer's denial specifically. Include your member ID, group number, claim number, and the specific plan language you're citing. State the exact relief you're requesting (reversal and payment). Keep the tone factual and professional — appeal reviewers see angry letters all day. Use ClaimSage's free appeal letter generator →
See a real example: How a $14,200 PT claim was overturned on first appeal →
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Submit the appeal — in writing, with delivery confirmation
Submit by certified mail or through the insurer's online portal with a read receipt. Keep a copy of everything you send. For ERISA plans, the plan must respond within 45 days of receiving your appeal. If they don't, that's considered a denial and you can escalate.
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If the internal appeal is denied — request an external review immediately
This is the step most people skip, and it's often the most effective. External reviewers are independent and overturn denials at significantly higher rates than internal reviewers. The form is usually included in your denial letter — fill it out and send it within the deadline.
What Your Appeal Letter Must Include
- Your member ID, group number, and the claim number from the EOB
- The specific denial reason and why you believe it's incorrect
- The specific plan clause the insurer cited — and why it doesn't apply in your case
- A letter from your treating physician with clinical justification
- Any peer-reviewed studies or clinical guidelines supporting the treatment
- Explicit statement of the relief you're requesting (reversal + payment)
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Frequently Asked Questions
How long do I have to file a health insurance appeal?
It depends on your insurer and the type of plan you have. For employer-sponsored plans (ERISA plans), you typically have 180 days from the date of the Explanation of Benefits to submit an internal appeal. For individual marketplace plans, most states give you 60 days. Medicare has 60 days from the MSN notice. Always check the notice of denial for the exact deadline — missing it can void your right to appeal.
What's the difference between an internal appeal and an external review?
An internal appeal is a complaint you file directly with your insurance company asking them to reconsider their decision. If the company upholds the denial, you can then request an external review — an independent third party (not your insurer) reviews the decision and makes a binding determination. External reviewers overturn denials about 35–50% of the time. It's the most underused tool in the appeals process.
What is an ERISA appeal and why does it matter?
ERISA (Employee Retirement Income Security Act) is a federal law that governs most employer-sponsored health plans. If your health insurance comes through work, your plan is almost certainly governed by ERISA. ERISA sets specific rules for the appeals process: your plan must give you at least 180 days to appeal, must provide a review process that doesn't just rubber-stamp the initial decision, and must give you written reasons for denial.
Can I appeal a denial even if I don't have all the medical records?
Yes — but get them as quickly as you can. You don't need everything before you file the initial appeal; many plans allow you to submit additional information during the review. A letter from your treating physician explaining the medical necessity of the denied service is often the single most persuasive piece of evidence you can include.
What are the most common reasons health insurers deny claims?
The five most common denial reasons are: (1) Prior authorization not obtained; (2) Out-of-network provider; (3) Not medically necessary; (4) Experimental or investigational treatment; (5) Coding errors or billing mistakes. Each requires a different strategy in your appeal letter.
Should I hire an insurance advocate or attorney for my appeal?
For routine claim denials under $5,000, a well-written appeal letter is usually sufficient. For high-value denials — surgery, expensive medication, long-term care — a medical billing advocate or healthcare attorney can significantly improve your odds. Advocates typically charge $200–$500/hour or take a contingency fee (25–35% of what they recover). ClaimSage's appeal letter generator gives you a professional-quality letter at no cost, which is a strong first step before engaging paid help.
What should I include in a health insurance appeal letter?
A strong appeal letter includes: (1) Your member ID, group number, and the claim number from the EOB; (2) A clear statement of what you're appealing and why you believe the denial is wrong; (3) A citation to the specific plan language the insurer is relying on; (4) Medical evidence — doctor's notes, peer-reviewed studies, clinical guidelines; (5) An explicit request for the exact relief you want; (6) A professional, factual tone. Generate one for free →
What happens after I file an external review?
The external review organization (ERO) has 45 days to issue a decision (urgent cases get a 72-hour turnaround). Their decision is binding on the health plan. If the external review upholds the denial, you can pursue arbitration, litigation, or a state insurance department complaint as a final recourse.