Claim Denied as Not Medically Necessary: How to Appeal

"Not medically necessary" is the single most common reason insurance companies deny claims — and also the most commonly overturned on appeal. Understanding the legal standard behind this phrase, why insurers apply it inconsistently, and how to counter it with the right evidence is the foundation of any successful appeal. Studies consistently show that 50 to 70 percent of medical necessity denials are overturned when patients appeal — and most people who receive a denial never appeal at all. The insurer is counting on that.

Why Insurers Deny Claims as Not Medically Necessary

Medical necessity is not a uniform standard. It varies by plan, by state, and by the specific guidelines an insurer uses. However, most health plan documents define it as treatment that is appropriate for the diagnosis or condition, consistent with the generally accepted standards of medical practice, not primarily for the convenience of the patient or provider, and the most cost-effective treatment available that adequately addresses the condition.

Insurers rely on proprietary utilization review tools — primarily InterQual and Milliman Care Guidelines — to evaluate treatment requests and submitted claims. These are population-based criteria designed to identify statistically "average" care. They do not automatically account for your individual comorbidities, treatment history, or your physician's clinical reasoning. The insurer's reviewer — often a nurse or non-specialist physician — applies these criteria to your records without examining you. This process is fast, inexpensive, and systematically biased toward denial.

Under ERISA (29 CFR § 2560.503-1) and the ACA, if your plan is an employer-sponsored or marketplace plan, the insurer's determination of medical necessity must be made in accordance with generally accepted standards of medical practice — not just their proprietary criteria. When your doctor's clinical judgment aligns with published guidelines from major medical societies, and the insurer denies anyway using internal criteria, you have strong grounds for appeal.

How to Appeal

Step 1: Get the Full Denial Details

Call the insurer and request the specific clinical criteria used to deny your claim, the name and specialty of the reviewing clinician, and a copy of the plan's medical necessity definition. Under ERISA (29 CFR § 2560.503-1), you are legally entitled to all of this information. If the denial letter does not identify the specific criterion you failed to meet, request that information in writing.

Step 2: Obtain a Physician Letter of Medical Necessity

This is the single most important document. The letter should state the diagnosis, explain why the treatment was necessary, describe what alternatives were considered and why they were insufficient, and directly address the insurer's stated denial reason. A generic letter is insufficient — the letter must engage with the specific criterion Cigna cited.

Step 3: Gather Clinical Guideline Support

Find the relevant guideline from the appropriate medical society. Quote the exact recommendation, evidence grade, and the criteria your case meets. A denial that contradicts a Class I AHA recommendation or an NCCN Category 1 guideline is very hard to sustain. Under the ACA, the insurer's utilization criteria should not supersede the established standards of the medical community.

Step 4: Request a Peer-to-Peer Review

Your physician can speak directly with the insurer's medical director. Many denials are overturned at this stage because the reviewing clinician was applying criteria without understanding your full clinical picture. The Mental Health Parity and Addiction Equity Act (MHPAEA) prohibits applying stricter medical necessity criteria to mental health and substance use disorder claims than to comparable medical or surgical claims — if your mental health claim was denied, request a non-quantitative treatment limitation analysis.

Step 5: File the Formal Internal Appeal Within 180 Days

Submit your appeal letter with all supporting documentation before the deadline. Send by certified mail and through the insurer's electronic portal if available. Keep copies of everything.

Step 6: Request External Independent Review: Complete Guide" class="auto-link">External Review if Denied

Under the ACA, you have the right to independent external review at no cost. External reviewers — who are independent clinicians paid regardless of outcome — overturn medical necessity denials at significantly higher rates than internal appeals. For mental health denials, request an NQTL comparative analysis and file a concurrent MHPAEA complaint with the Department of Labor.

What to Include in Your Appeal

• The denial letter with the specific reason code and policy provision cited
• A letter of medical necessity from your treating physician, addressing the insurer's stated rationale directly
• Your complete relevant medical records (diagnosis, treatment history, lab results, imaging)
• The insurer's clinical policy bulletin or criteria used to deny (request this in writing)
• Peer-reviewed clinical practice guidelines from the relevant specialty society with the specific recommendation and evidence grade
• Published studies supporting the treatment's efficacy for your specific diagnosis
• Records of any prior treatments attempted and their outcomes
• Any peer-to-peer review notes if one was already attempted

Fight Back With ClaimBack

A not-medically-necessary denial is one of the most winnable appeals — but only when you present the right evidence in the right format. The combination of a strong physician letter, specific guideline citations, and direct engagement with the insurer's denial criteria gives reviewers and external IROs the evidence they need to reverse the decision. ClaimBack analyzes your specific denial reason, matches it against clinical guidelines, and generates a professional appeal letter built for your case 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