How to Appeal a Health Insurance Denial: What to Say, What to Send, What Actually Works

You opened the letter. It said something like "adverse benefit determination" or "not medically necessary" or "prior authorization denied." Maybe it cited a code like CO-50. Maybe it just said your plan doesn't cover this service. Either way, the message was clear: we're not paying.

What the letter did not say is that you have the right to appeal, that appeals succeed at a surprisingly high rate, and that the insurer is banking on you not knowing either of those things. Denials are, in part, a filter. The process is designed to be confusing enough that most people give up.

This guide is about not giving up — and what specifically to say when you don't.

Before You Write a Single Word: Request a Peer-to-Peer Review

Most people skip this step because they've never heard of it. That's a mistake.

A peer-to-peer review is a phone call between your doctor and the insurance company's medical reviewer. It's not a hearing, it's not a formal appeal — it's a physician-to-physician conversation about whether the treatment was appropriate. And it overturns approximately 69 to 82 percent of prior authorization denials when requested.

Your doctor does the work here, not you. Your job is to ask them to do it.

That's it. One phone call from your doctor. If it works, you're done. If it doesn't, you proceed to the written appeal — but now you've documented that you tried, which strengthens your record.

This step only applies to prior authorization denials. If your claim was denied after the care was already provided, skip ahead to the written appeal.

Why Most Appeal Letters Fail Before They're Read

The internet will tell you to "document everything" and "be persistent." That's technically true and completely useless. Here's what actually matters.

Insurance appeal reviewers are not on your side. They're reading your letter looking for a reason to close the file, not a reason to pay. Emotional language — "I've been struggling for years," "this is devastating to my family," "I don't know what I'll do" — gets noted and ignored. It signals that you don't know the process. Reviewers are trained to evaluate medical necessity criteria, not hardship.

What works is using the insurer's own language against them. That means:

Quoting the plan's definition of "medically necessary" verbatim, then showing, element by element, that your treatment meets it. The definition is in your Summary Plan Description. Get a copy if you don't have it — you're legally entitled to one within 30 days of asking.

Identifying the clinical criteria system the insurer used to deny you — usually InterQual or MCG (formerly Milliman Care Guidelines) — and showing that your case satisfies those criteria. This is the vocabulary that tells a reviewer you know what you're doing.

Citing the relevant federal regulation by number. For internal appeals, that's typically 29 CFR §2560.503-1 (ERISA) or 45 CFR §147.136 (ACA plans). Including these signals that you know your procedural rights, which matters for how carefully your letter gets reviewed.

Generic letters — the kind you find by Googling "free appeal letter template" — are identified immediately. They're form letters and reviewers have seen thousands of them. The vocabulary is wrong. The structure is wrong. They don't cite the right standards. They get denied.

The Opening That Sets the Tone

Every strong appeal letter does the same thing in the first paragraph: it identifies the denial, invokes your rights, and signals that you know the process. Here's what that looks like:

Then, in the second paragraph, you address medical necessity directly:

Notice what this doesn't do: it doesn't explain how much you've suffered. It doesn't ask for sympathy. It treats the reviewers as the professionals they are and gives them what they need to justify a reversal. A reviewer who wants to approve your appeal needs ammunition to override their own denial. Your job is to give it to them.

The Documents That Win Appeals

The letter is only half of it. What you attach determines whether the letter works.

At minimum, every appeal should include:

A letter of medical necessity from your doctor. Not a form letter. An actual letter from the physician, on letterhead, explaining the diagnosis, what was tried before, why this treatment is appropriate, and what the clinical evidence says. The more specific, the better. "Standard of care" means nothing. "2023 ACC/AHA Guidelines for Management of Heart Failure, Section 7.3, recommend [TREATMENT] for patients with [SPECIFIC CRITERIA], which this patient meets" means something.

Your relevant medical records. The records that document the condition, the prior treatments tried, and the outcomes. Don't send your entire medical history. Send the records that support the specific argument you're making in the letter.

Relevant clinical guidelines or peer-reviewed research. If a major medical society has published guidelines that recommend your treatment for your condition, print them and attach them. The insurer's own clinical criteria often cite the same sources. Make it easy for the reviewer to connect the dots.

A copy of the denial letter itself. Include it. Keeps everything in one package and prevents any "we don't have the original denial on file" delays.

What to Do When They Deny You Again

A second denial is not the end. It's actually where things get more interesting.

After two internal denials, you have the right to request an external independent review. An independent reviewer has no financial relationship with your insurer, and their decision is binding — the insurer cannot ignore it. External reviews overturn denials roughly 50% of the time.

To request an external review, you typically submit a request form (available from your insurer or state insurance department) within four months of the final internal denial. The insurer must pay for the review. You don't.

While your appeal is pending, there are two other levers worth pulling simultaneously:

File a complaint with your state insurance commissioner. This is not a lawsuit. It's an administrative complaint that puts your insurer on notice that a regulator is watching. Insurers take these seriously because patterns of complaints can trigger audits. The complaint itself often prompts a second review of your case. Your state's insurance department website has the form.

Escalate to your employer's HR department if your plan is employer-sponsored. HR has a relationship with the insurer you don't have. A call from HR asking why an employee's claim keeps getting denied sometimes moves faster than three months of formal appeals.

The Deadlines You Cannot Miss

Every step in this process has a deadline. Miss one and you may lose your right to appeal entirely.

For most plans: you have 180 days from receiving a denial to file an internal appeal. Don't wait. The sooner you file, the more time your doctor has to provide the strongest possible supporting documentation.

For urgent care appeals: you have 72 hours to request an expedited review. If your situation is time-sensitive — ongoing treatment, a surgery scheduled soon, a medication you're currently taking — say so explicitly and request expedited review in your letter.

For external review: you typically have 4 months from the final internal denial. The insurer must notify you of this right and the deadline when they issue the denial. Check that letter.

When in doubt, file early, send by certified mail with return receipt, and keep a copy of everything.

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