Can Insurance Deny Medically Necessary Treatment?

Yes — insurance companies can and regularly do deny treatment that your doctor says is medically necessary. According to a KFF analysis of ACA marketplace data, approximately 17% of in-network claims are denied, and medical necessity disputes account for a significant share of those denials. However, the fact that an insurer can deny a claim does not mean the denial is correct or that you are without recourse. External Independent Review: Complete Guide" class="auto-link">External reviewers overturn medical necessity denials approximately 40 to 65 percent of the time when proper documentation is submitted.

Why Insurers Deny "Medically Necessary" Treatment

The treatment doesn't meet the insurer's internal criteria. Insurers maintain clinical policy bulletins (CPBs) and use standardized review tools like Milliman or InterQual that are often more restrictive than what treating physicians and specialty societies consider appropriate. These are the insurer's own criteria — not medical standards.

The insurer's reviewer disagrees with your doctor. An insurance company medical reviewer — who has typically never examined you — concludes that a less intensive or less expensive treatment is sufficient. This is one of the most frequently reversed denial types on appeal.

Insufficient documentation. The claim lacks detailed clinical records needed to demonstrate necessity under the insurer's criteria. Blood test results, imaging studies, specialist assessments, and a specific physician rationale are often required but not included in the initial claim submission.

Step therapy or Prior Authorization Denied: How to Appeal" class="auto-link">prior authorization not completed. The insurer denies because you haven't tried a less expensive alternative or because prior authorization wasn't obtained before treatment.

Experimental or investigational classification. The insurer denies a treatment supported by clinical evidence but not approved in their internal guidelines — common with newer cancer treatments, gene therapies, and off-label drug uses.

How to Appeal

Step 1: Get the Insurer's Clinical Policy Bulletin

Request the CPB the day you receive your denial — you are legally entitled to this under ERISA 29 CFR § 2560.503-1 and ACA 45 CFR § 147.136. This document specifies exactly what criteria the insurer requires. Your appeal must address these criteria directly — not just argue that the treatment is generally appropriate.

Step 2: Get a Targeted Physician Letter

Your treating physician's letter is the foundation of the appeal. It must address each criterion in the insurer's CPB specifically, include objective data (lab values, imaging measurements, functional scores), explain the clinical consequences of denial, cite published clinical guidelines from relevant specialty societies, state that the treatment is the standard of care, and directly rebut the insurer's stated denial reason. A generic letter will not succeed.

Step 3: Cite Clinical Practice Guidelines

Identify the relevant specialty society guidelines (NCCN for oncology, AAN for neurology, AHA/ACC for cardiology, ASAM for substance use, APA for psychiatry). If the insurer's CPB criteria are more restrictive than published guidelines, make this discrepancy explicit — it is one of the strongest grounds for appeal.

Step 4: Request Peer-to-Peer Review

Ask your treating physician to speak directly with the insurer's medical director. Many medical necessity denials are reversed during these conversations because the treating physician can present clinical nuances that written records don't convey. This is particularly effective when the insurer's reviewer lacks specialty expertise.

Step 5: File the Internal Appeal

Write your appeal letter addressing every denial reason specifically with clinical evidence and regulatory citations under ACA § 2719 and ERISA § 1133. Submit within 180 days for most commercial plans. For mental health and substance use disorder denials, invoke Mental Health Parity Act (MHPAEA) Explained" class="auto-link">MHPAEA § 1185a — insurers cannot apply more restrictive criteria than for comparable medical/surgical benefits.

Step 6: Escalate if Denied

Request free external review under ACA 45 CFR § 147.136(d) — an independent physician with no insurer affiliation evaluates your case. File within 4 months of the final internal denial. For urgent situations, request expedited review within 72 hours under 45 CFR § 147.136. For ERISA employer plans, consult an ERISA attorney about federal court options under ERISA § 502(a)(1)(B) after administrative exhaustion.

What to Include in Your Appeal

• Denial letter with the specific clinical criteria or policy provision cited
• Insurer's clinical policy bulletin — request immediately on denial
• Treating physician's detailed letter of medical necessity addressing the CPB criteria
• Clinical practice guidelines from relevant specialty societies
• Complete medical records: diagnosis, treatment history, test results, imaging
• Peer-reviewed literature if the insurer claims the treatment is experimental
• Documentation of failed prior treatments if step therapy is the issue

Fight Back With ClaimBack

Medical necessity denials succeed only when patients don't fight back. Well-prepared appeals with proper clinical documentation and regulatory citations succeed at meaningful rates. ClaimBack generates a professional appeal letter in 3 minutes, addressing your insurer's specific CPB criteria and citing the clinical guidelines and federal statutes that apply to your denial. 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