How to Appeal an Insurance Denial: Step-by-Step Guide

Your Claim Was Denied. Here's What to Do.

A denied claim is not a final answer. It's a starting point. Studies show that 50-60% of appealed denials are overturned, yet fewer than 1% of denied claims are ever appealed. The payers know this. They're counting on you to write it off.

Don't. This guide walks you through every step of the appeal process — from reading the denial notice to escalating through external review. Each step ends with a specific action you can take right now.

Step 1: Read the Denial Notice Carefully

Before you do anything else, pull the denial notice (EOB or ERA) and find these four things:

1. The denial reason code. This is the CARC code — CO-4, CO-97, PR-1, CO-197, etc. It tells you exactly why the claim was denied.
2. The payer name and claim number. You'll need both for the appeal letter and to track the claim.
3. The date on the notice. Your appeal clock starts here. Miss the deadline, lose the appeal.
4. The denied CPT code(s) and date of service. Know exactly which services were denied — sometimes only part of a claim is denied.

Not sure what your denial code means? Ask Pika — paste your denial code and get a plain-English explanation with the exact fix.

Step 2: Know Your Deadline

Every payer has a timely filing limit for appeals. Miss it and you lose your right to appeal, regardless of how strong your case is. Here are the deadlines for major payers:

Payer	Appeal Deadline	Notes
Medicare	120 days	Level 1 Redetermination from your MAC
UnitedHealthcare	90 days	From date on EOB/ERA
Aetna	60 days	From date on EOB/ERA
Cigna	90 days	180 days for some plan types
Humana	60 days	From date on EOB/ERA
BCBS	60-180 days	Varies by state — check your plan
Medicaid	Varies by state	Typically 30-90 days, check your state's Medicaid manual

Action: Look at the date on your denial notice right now. Count the days. Put the appeal deadline on your calendar. If you're within 10 days of the deadline, file today.

Step 3: Identify WHY It Was Denied

The denial reason code tells you the fix. Some denials need an appeal. Others just need a corrected claim resubmission. Here are the most common denial codes and what to do about each:

CO-4: Modifier Missing or Incorrect

A modifier is wrong or missing on the claim. Most common cause: modifier 25 placed on the wrong line (e.g., on a G-code instead of the E/M code).

Fix: Correct the modifier placement and resubmit. This is a corrected claim, not an appeal.

CO-97: Bundling Denial

The payer says one code is included in the payment for another code on the same claim. Check the CCI edits for your code pair.

Fix: If the codes are legitimately separate services, add modifier 59 or the appropriate X modifier (XE, XS, XP, XU) and resubmit. If they're truly bundled, drop the lower-paying code.

PR-1: Deductible Not Met

This is patient responsibility, not a claim error. The claim processed correctly — the patient owes this amount.

Fix: Bill the patient. No appeal needed. If you believe the deductible was already met, call the payer to verify the patient's accumulator.

CO-16: Missing Information

Something is missing on the claim form — diagnosis code, NPI, demographics, or place of service.

Fix: Find the missing field, correct it, and resubmit as a corrected claim.

CO-197: Prior Authorization Required

The service required prior auth and none was obtained (or it expired). This is one of the most common — and most appealable — denials.

Fix: Request retroactive authorization if the payer allows it. If not, appeal with documentation showing the service was medically necessary and that delay would have harmed the patient.

CO-50: Not Medically Necessary

The payer is saying the service wasn't warranted based on the diagnosis or clinical information submitted. This is the denial that requires the strongest appeal.

Fix: Appeal with clinical documentation. Cite the payer's own clinical policy criteria (see Step 4). This is where you win or lose.

Paste your specific denial code into Ask Pika and get the exact fix for your situation — including whether to resubmit or appeal.

For a complete reference of all denial codes, see our denial codes guide.

Step 4: Gather Your Documentation

A strong appeal is built on documentation, not arguments. Before you write the appeal letter, collect:

1. Medical records for the date of service. The clinical note, any test results, vitals, and relevant history that support the medical necessity of the service.
2. The payer's own clinical policy. This is your most powerful weapon. Every major payer publishes their coverage criteria:
   • Medicare: Local Coverage Determinations (LCDs) and National Coverage Determinations (NCDs) on the CMS website
   • UnitedHealthcare: UHC Medical Policies and Coverage Determination Guidelines
   • Aetna: Clinical Policy Bulletins (CPBs)
   • Cigna: Coverage Policies
   • Humana: Medical Coverage Policies
3. Peer-reviewed evidence. If the payer's own policy doesn't cover your case, published clinical studies and specialty society guidelines strengthen your appeal.
4. Timeline of conservative treatment. For surgical or escalated-care denials, document the progression: what you tried first, why it failed, and why the denied service was the appropriate next step.

Need help finding the payer's specific policy for your procedure? Ask Pika — describe your denial and Pika will point you to the right policy criteria.

Step 5: Write the Appeal Letter

Your appeal letter needs to be clear, specific, and cite the payer's own criteria. Here's the structure:

Appeal Letter Template

[Your Practice Letterhead]

Date: [Today's date]

To: [Payer name] Appeals Department
Re: Appeal of Denied Claim
Patient: [Patient name], DOB [Date of birth]
Member ID: [Member ID number]
Claim Number: [Claim number from denial notice]
Date of Service: [Date of service]
CPT Code(s): [Denied CPT code(s)]
Denial Reason: [CARC code and description]
Denial Date: [Date on denial notice]

Dear Appeals Committee,

I am writing to appeal the denial of [CPT code] for [patient name] on [date of service]. The denial reason given was [denial code: description]. I respectfully request reconsideration based on the following clinical justification.

[Clinical Justification — 1-2 paragraphs]
Describe the patient's condition, the clinical decision-making process, and why the service was medically necessary. Be specific: diagnosis, severity, what was tried previously, and why this service was the appropriate intervention.

[Policy Citation — 1 paragraph]
Per [Payer name]'s own clinical policy [policy name/number], this service meets coverage criteria when [quote the specific criteria the patient meets]. The attached documentation demonstrates that the patient meets [criterion 1], [criterion 2], and [criterion 3].

Enclosed: [List all supporting documents — clinical notes, test results, prior treatment records, policy excerpt]

I respectfully request that this claim be reconsidered and processed for payment. Please contact me at [phone] with any questions.

Sincerely,
[Provider name, credentials]
[NPI number]
[Practice name and address]

Want a pre-drafted appeal letter for your specific denial? Ask Pika: "Write an appeal letter for [denial code] on [CPT code] from [payer name]" — and get a ready-to-customize draft in seconds.

Step 6: Submit the Appeal

How you submit matters. Always use two channels for a paper trail:

1. Fax — for speed. Keep the fax confirmation page as proof of submission.
2. Certified mail — for a legal paper trail. Request return receipt.

Where to send appeals by payer

• Medicare: Your Medicare Administrative Contractor (MAC). The address is on the ERA/EOB. Common MACs: Novitas Solutions, Palmetto GBA, First Coast Service Options, National Government Services, WPS Government Health Administrators.
• UnitedHealthcare: Address on the EOB, or submit via the UHC Provider Portal.
• Aetna: Address on the EOB. Many plans also accept appeals via the Availity portal.
• Cigna: Cigna Appeals, PO Box 188011, Chattanooga, TN 37422.
• Humana: Address on the EOB, or fax to the number listed on the denial letter.
• BCBS: Varies by state plan — always use the address on the EOB.

Action: Submit today. Don't wait. Every day you wait is a day closer to the deadline.

Step 7: If the First Appeal Fails

A first-level denial is not the end. Every payer has multiple levels of appeal, and the odds improve at each level because an independent reviewer gets involved.

Medicare Appeal Levels

Medicare has 5 levels of appeal. Most claims are resolved at Level 1 or 2:

1. Level 1 — Redetermination. Filed with your MAC. Must be filed within 120 days. Decision within 60 days. About 75% of appealed claims are overturned here.
2. Level 2 — Reconsideration. Filed with a Qualified Independent Contractor (QIC). Must be filed within 180 days of the Level 1 decision. Independent review — not the same entity that denied it.
3. Level 3 — Administrative Law Judge (ALJ). Hearing before an ALJ. Amount in controversy must exceed $180 (2026 threshold). This is where you present your case in person or by phone.
4. Level 4 — Medicare Appeals Council. Review of the ALJ decision. Rarely needed.
5. Level 5 — Federal District Court. Judicial review. Amount in controversy must exceed $1,840 (2026). Extremely rare.

Commercial Payer Appeal Levels

1. First-level internal appeal. Reviewed by the payer's own medical staff (different from the original reviewer).
2. Second-level internal appeal. Some payers offer a second internal review. Check your plan documents.
3. External review. An Independent Review Organization (IRO) reviews the denial. The IRO has no affiliation with the payer. Their decision is binding on the payer in most states. This is required under the ACA for all non-grandfathered plans.
4. State insurance commissioner complaint. If the payer ignores the IRO decision or you believe they acted in bad faith, file a complaint with your state's Department of Insurance.

Action: If your first appeal was denied, don't stop. File the next level immediately. The higher you go, the more independent the review becomes — and the more likely you are to win.

Common Mistakes That Kill Appeals

• Missing the deadline. The single most common reason appeals fail. Calendar it the day you receive the denial.
• Not citing the payer's own policy. Generic "this was medically necessary" letters get denied. Quote their specific criteria and show how the patient meets each one.
• Insufficient clinical documentation. "Patient was seen and treated" is not enough. Include specific findings, test results, and clinical reasoning.
• Appealing when you should resubmit. CO-4 (modifier error), CO-16 (missing info), and CO-18 (duplicate) are corrected claim resubmissions, not appeals. Appealing wastes time.
• Not escalating. If your first appeal fails, file the next level. Many providers give up after one denial. The payers are counting on this.

Don't fight denials alone. Ask Pika your specific denial scenario and get a step-by-step appeal strategy in seconds. Try: "My CO-50 denial for 99215 from UnitedHealthcare was upheld on first appeal. What do I do next?"