How to Appeal a Denied Insurance Claim: A Step-by-Step Guide for Billing Teams

Industry estimates consistently put the first-pass denial rate at around 12% — and that number has been climbing for years as payers tighten clinical and administrative edits. The harder truth: an estimated 35–65% of those denials are never appealed. They become permanent write-offs, not because the money isn't recoverable, but because the manual labor to fight each claim is too expensive relative to its value.

That math changes when you have a repeatable process. Here's a step-by-step approach billing teams can follow for any denied claim.

Step 1: Read the remittance, not just the denial code

Every remittance advice (835 or paper EOB) contains at least one Claim Adjustment Reason Code (CARC) — the primary denial reason — and usually one or more Remittance Advice Remark Codes (RARC) that add detail. Don't stop at the CARC. A denial coded CO-16 (missing information) is meaningless without the RARC that tells you exactly which field is missing.

Mapping both codes to the actual denial reason — not just the category — is the most important step in the process. Refer to the denial code guide for plain-English explanations of the most common codes.

Step 2: Determine whether to appeal or correct-and-resubmit

Not every denial is an appeal. There are two paths:

• Correct and resubmit — for claims with a fixable billing or coding error (wrong modifier, missing field, wrong payer). These aren't appeals; the original claim was defective and needs to be refiled correctly.
• Formal appeal — for claims that were billed correctly but denied for coverage, medical necessity, prior auth, or timely filing reasons. These require a written appeal with supporting documentation.

Sending a formal appeal on a claim that just needs a modifier correction wastes time and delays payment. Know which path you're on before you write anything.

Step 3: Pull the payer's published medical policy

For medical necessity, prior authorization, and coverage denials, the most important document in your appeal is the payer's own published policy for the procedure. Every major commercial payer publishes medical policies on their provider portal. Medicare uses Local Coverage Determinations (LCDs) and National Coverage Determinations (NCDs).

The policy tells you exactly what the payer requires to approve the service. Your appeal needs to show, criterion by criterion, how the patient's clinical record meets those requirements. A generic "this was medically necessary" letter almost never overturns a denial — citing the carrier's own criteria does.

Step 4: Gather the supporting documentation

The documentation package depends on the denial type:

• Medical necessity (CO-50, CO-167): Progress notes, lab results, imaging reports, evidence of prior conservative treatment — whatever shows the clinical basis for the service.
• Prior authorization (CO-197): Authorization confirmation numbers, application submission records, or emergency exception documentation.
• Timely filing (CO-29): Clearinghouse acceptance reports, original submission confirmations, or evidence of a prior on-time submission that was lost.
• Coordination of benefits (CO-22): Primary payer's EOB, proof of payer order, updated COB information.

Step 5: Write a letter that addresses the specific denial reason

The appeal letter should:

• State the claim number, member ID, date of service, and the specific denial code being appealed.
• Quote the relevant payer policy or coverage criteria.
• Walk through the supporting documentation point-by-point, showing how each criterion is met.
• Explicitly request reconsideration and payment.
• Include the filing deadline and note when timely response is required.

Step 6: Track the filing deadline and follow up

Every payer has an appeal filing deadline — typically 60 to 180 days from the date of the denial. Missing it forfeits the right to appeal entirely. Tracking each appeal's deadline, submission date, and outcome is as important as writing the letter itself.

If you don't receive a decision within the payer's stated turnaround, follow up by phone and document the call reference number. Escalate to a second-level appeal if the first is denied and the claim value justifies it.

The bottleneck: volume

The process above works — but at $25–118 in labor per appeal, it only makes economic sense for higher-dollar denials. That's why the 35–65% of denials that never get appealed are mostly the small- and mid-dollar claims: the math doesn't support the work.

That's the problem Remitavo addresses: the same payer-specific, policy-citing appeal letter — generated in seconds from the remittance file. See the sample appeal to read a real output.