How to Appeal a Health Insurance Denial

Receiving a health insurance denial letter is one of the most disorienting moments in healthcare. You followed the rules, got the care you needed, and now your insurer is refusing to pay — often citing reasons that feel arbitrary or impossible to decipher. The good news is that denials are not final: federal law and most state laws give you the explicit right to appeal, and a well-constructed appeal overturns denials far more often than most patients realize.

What does a health insurance denial letter actually mean?

Before you can fight a denial, you need to understand exactly what type of denial you received. Insurers are required under the Affordable Care Act (ACA) to send an Explanation of Benefits (EOB) and a denial notice that includes the specific reason for denial, the clinical or contractual criteria used, and instructions for how to appeal.

Common denial reason codes and what they mean:

• Medical necessity denial: The insurer decided the service was not "medically necessary" under their clinical criteria, even if your doctor ordered it.
• Prior authorization denial: The service required pre-approval that was not obtained, or was obtained but later deemed insufficient.
• Out-of-network denial: The provider was not in your plan's network, and your plan does not cover out-of-network services at the billed rate.
• Experimental or investigational denial: The insurer classified the treatment as unproven or not standard of care.
• Coding or administrative denial: A billing error — wrong procedure code, missing modifier, or incorrect diagnosis code — triggered an automatic rejection.

Your denial letter must include the specific ICD-10 diagnosis codes and CPT procedure codes at issue. If it doesn't, call member services immediately and request the complete clinical rationale in writing. You cannot build an effective appeal without this information.

What are your legal rights when a health insurance claim is denied?

Under the ACA and the Employee Retirement Income Security Act (ERISA), you have federally protected rights in the appeals process. Understanding these rights is not optional — it's your foundation.

• Internal appeal right: You have the right to at least one internal appeal reviewed by someone who was not involved in the original denial decision.
• External review right: If your internal appeal is denied, you have the right to an Independent Review Organization (IRO) review — a binding, third-party decision that the insurer must accept.
• Urgent care timeline: For urgent or ongoing treatment, insurers must resolve expedited appeals within 72 hours.
• Standard internal appeal timeline: Insurers must resolve standard internal appeals within 30 days for pre-service denials and 60 days for post-service claims.
• No cost for appeals: You cannot be charged a fee to file an internal appeal or request external review.

If your plan is self-funded (common with large employers), ERISA governs your rights. If your plan is purchased through the marketplace or is a fully insured employer plan, both federal ACA rules and your state's insurance regulations apply — and state protections are often stronger.

How do you write a strong health insurance appeal letter?

Your appeal letter is the most important document in this process. It should be factual, specific, and supported by clinical evidence. Do not write an emotional narrative — write a structured argument.

1. State the basics up front: Include your name, member ID, date of service, claim number, the specific CPT and ICD-10 codes being disputed, and the denial reason code from your EOB.
2. Directly address the denial reason: If the denial says the service was not medically necessary, your letter must argue — specifically — why it was. Reference the insurer's own clinical criteria by name if you can find them (many plans publish their medical policies online).
3. Attach a Letter of Medical Necessity (LMN): Ask your treating physician to write a letter that documents your diagnosis, the treatment, why alternatives were tried or are not appropriate, and the evidence base (peer-reviewed studies, clinical guidelines from organizations like the American College of Obstetricians and Gynecologists or the American Academy of Pediatrics) supporting the treatment.
4. Cite clinical guidelines: Reference specific, named clinical guidelines — for example, "According to ACOG Practice Bulletin No. 212, this intervention is standard of care for patients with this diagnosis." Vague claims carry no weight; specific citations do.
5. Request the plan's clinical criteria: Under ERISA and ACA rules, you are entitled to the specific clinical criteria the insurer used to deny your claim. If you don't already have them, request them and compare them point-by-point in your letter.
6. State what you are requesting: End with a clear, specific ask — that the claim be approved and paid at the applicable in-network rate, for example.

Send your appeal by certified mail with return receipt, and keep copies of everything. Note the date you sent it and calculate your insurer's legally required response deadline from that date.

What evidence should you gather to support your insurance appeal?

A letter alone rarely wins an appeal. You need a documented evidence package that makes it harder for the reviewer to maintain the denial than to reverse it.

• Complete medical records: Request your full records from the treating provider — including physician notes, lab results, imaging reports, and operative reports. HIPAA gives you the right to these records, and providers must supply them.
• Peer-reviewed clinical studies: PubMed (pubmed.ncbi.nlm.nih.gov) is a free, searchable database of medical research. Studies from respected journals that support the medical necessity of your treatment are powerful attachments.
• Clinical practice guidelines: Published guidelines from major specialty societies carry significant weight. Download and attach the relevant section.
• Prior authorization documentation: If prior auth was obtained, include every piece of documentation — approval letters, reference numbers, phone call logs.
• Previous EOBs: If the insurer paid for the same service before, attach those EOBs. Inconsistent claim adjudication is a strong argument.
• Second physician opinion: A letter from a second qualified physician supporting the necessity of care adds independent clinical weight.

What happens if your internal appeal is denied — how does external review work?

If your insurer upholds the denial after your internal appeal, do not stop. External review is your most powerful tool, and insurers lose a significant percentage of external reviews.

Here's how the external review process works:

1. Request external review within the deadline. You typically have four months (60 days under federal rules, longer under many state rules) from the date of the final internal denial to request external review. Missing this deadline can forfeit your rights.
2. Your insurer assigns an IRO. The Independent Review Organization is accredited by URAC or NCQA and is prohibited from having any financial relationship with your insurer.
3. Submit your complete evidence package. You have the right to submit additional evidence directly to the IRO — include everything from your internal appeal plus anything new.
4. The IRO issues a binding decision. Under federal law, the insurer must comply with the IRO's decision. If the IRO overturns the denial, your claim must be paid.
5. If you need expedited review, request it. For ongoing or urgent treatment, expedited external review decisions must be issued within 72 hours.

If external review fails — which is uncommon for well-documented medical necessity cases — your remaining options include filing a complaint with your state insurance commissioner, consulting a patient advocate or attorney who specializes in insurance law, or, for ERISA plans, pursuing litigation in federal court.

How can a patient advocate help you appeal a denied insurance claim?

Professional patient advocates and medical billing advocates specialize in exactly this process. They know how to read EOBs, identify the actual reason behind a denial code, locate the relevant clinical criteria, and construct appeals that speak the insurer's own language. For complex denials — especially those involving high-cost maternity care, NICU stays, surgical complications, or experimental treatments — professional help often makes a decisive difference.

When choosing an advocate, look for:

• Board certification through the Patient Advocate Certification Board (PACB) or membership in the Alliance of Professional Health Advocates (APHA)
• Experience with your specific denial type (medical necessity vs. out-of-network vs. coding error)
• Clear fee structures — many advocates work on contingency, taking a percentage of the amount recovered
• Familiarity with your state's specific insurance regulations and appeal timelines