Insurance companies deny roughly 17% of all healthcare claims — and 65% of those denials are never appealed, leaving billions in earned revenue permanently uncollected. Whether you're a medical billing specialist, a practice manager, or a provider handling your own revenue cycle, this guide explains exactly how to appeal a healthcare insurance denial and recover what you've earned.
Why Healthcare Claims Get Denied
Before you can write an effective appeal letter, you need to understand why the claim was denied. Every denial notice includes one or more Claim Adjustment Reason Codes (CARC) — often listed as "CO" codes — that explain the payer's rationale. The most common denial reasons fall into five categories:
| Denial Code | Meaning | Category |
|---|---|---|
| CO-50 | Not medically necessary — the payer's clinical criteria were not met | Medical Necessity |
| CO-197 / CO-198 | Prior authorization not obtained, or auth limit exceeded | Authorization |
| CO-4 | Procedure code is inconsistent with modifier used | Coding Error |
| CO-11 | Diagnosis is inconsistent with the procedure performed | Coding Error |
| CO-16 | Missing or incomplete claim information | Administrative |
| CO-97 | Service bundled into another procedure (NCCI edit) | Bundling |
| CO-29 | Timely filing limit exceeded | Timely Filing |
| CO-22 | Coordination of benefits — another payer may be primary | COB |
Identifying the correct denial code is the first and most important step — because the appeal strategy for a CO-50 (medical necessity) denial is completely different from a CO-4 (coding error) denial. Coding errors may require a corrected claim rather than a formal appeal letter.
Pro tip: Not every denial should become an appeal letter. CO-4, CO-11, and CO-16 denials are often best resolved by submitting a corrected claim — not a formal appeal. Submitting an appeal for a correctable coding error wastes time and delays payment.
The 6-Step Healthcare Claim Appeal Process
Once you've confirmed that a formal appeal is the right path, here is the standard insurance denial appeal process — from initial review to final escalation.
Review the Explanation of Benefits (EOB)
Pull the payer's EOB or remittance advice. Identify the specific CARC/RARC denial codes, the service lines affected, and the dollar amount at stake. Confirm the denial date — this is when your appeal deadline clock starts. Document the claim number, patient member ID, and the exact denial reason verbatim from the EOB.
Determine Your Appeal Deadline
Every payer has a different filing window — and missing it means the revenue is gone permanently. UnitedHealthcare's 65-day deadline is the shortest in the industry. Anthem and Cigna allow 180 days. Medicare Part B allows 120 days. Check the denial letter — the deadline is always disclosed on the notice. Log it immediately and set a reminder to act at least 30 days before the deadline.
Gather Supporting Documentation
For medical necessity denials: pull physician progress notes, lab results, imaging reports, treatment history showing failed conservative alternatives, and any clinical evidence directly tied to the denial. For authorization denials: locate the prior auth request, approval confirmation, or peer-to-peer log. For coding denials: pull the operative report or medical record to support the procedure code used. Organize all documents before drafting the letter.
Write the Appeal Letter
A complete appeal letter is not a generic complaint — it's a clinical and administrative argument tailored to the payer's specific denial criteria. Reference the payer's own medical policies. Cite the clinical guidelines they use (InterQual® for UHC, MCG for Aetna). State your argument in plain medical language. Keep it factual, not emotional. We cover exactly what to include below.
Submit Via the Payer's Preferred Method
UnitedHealthcare requires portal submission via UHCProvider.com. Anthem prefers Availity. Aetna accepts portal, fax, and mail. Always get confirmation of submission — a portal receipt number or fax confirmation page. This is critical proof if the payer claims non-receipt. Send the complete packet: appeal letter + all supporting documentation together, clearly labeled with the claim number.
Follow Up and Escalate if Needed
If the internal appeal is denied or you receive no response within 30 days, escalate. Request an external independent review — external reviewers overturn internal appeal decisions 40–60% of the time. For clinical denials, simultaneously request a peer-to-peer review — a physician-to-physician call with the payer's medical director that overturns 65–85% of medical necessity denials when done correctly. For Medicare, escalate through the 5-level appeals process (Redetermination → Reconsideration → ALJ Hearing).
What to Include in a Healthcare Denial Appeal Letter
The quality of your appeal letter is the single biggest driver of overturn rates. A vague, generic letter is easy to deny a second time. A specific, evidence-backed letter that speaks the payer's language forces the reviewer to engage with your argument. Here's what every appeal letter must contain:
Appeal Letter Checklist
- ✓ Patient identifying info: Full name, date of birth, insurance member ID, and group number
- ✓ Claim details: Claim number, date of service, billed procedure code(s) (CPT), and diagnosis code(s) (ICD-10)
- ✓ Denial code and reason: State the exact CARC code from the EOB and the payer's stated reason verbatim
- ✓ Clear statement of dispute: "We are formally appealing the denial of claim [#] for the following reason: [specific argument]"
- ✓ Clinical evidence: Summary of medical records supporting medical necessity, tailored to the denial code
- ✓ Payer criteria reference: Cite the payer's specific clinical criteria by name (e.g., "Per InterQual® Acute Care criteria for [condition]...") — this is critical for UnitedHealthcare, Aetna, and Cigna
- ✓ Failed alternatives (if applicable): For medical necessity — document conservative treatments tried and failed, with specific dates, doses, and outcomes
- ✓ Provider contact & NPI: Provider name, NPI number, practice address, phone, and signature
- ✓ Attachments listed: Explicitly list every document attached (e.g., "Exhibit A: Progress notes 01/15/2026 — 02/10/2026")
- ✓ Appeal deadline awareness: Include language such as "This appeal is submitted within the [X]-day filing window per [Payer] policy"
Common mistake: Submitting a generic appeal letter without referencing the payer's clinical criteria. UnitedHealthcare uses InterQual®. Aetna uses MCG (Milliman Care Guidelines). Cigna uses its own proprietary criteria. Each payer's medical reviewers are trained to evaluate appeals against their specific tool — if you don't speak their language, you're writing for a different audience.
Appeal Deadlines by Payer
Missing a filing deadline is permanent and irreversible — the revenue cannot be recovered after the deadline has passed. Here are the appeal filing deadlines for the largest commercial payers:
| Payer | Internal Appeal Deadline | Submission Method |
|---|---|---|
| UnitedHealthcare | 65 calendar days (shortest in industry) | UHCProvider.com portal (required) |
| Aetna | 180 calendar days | Availity portal, fax, or mail |
| Cigna | 180 calendar days | Cigna for Health Professionals portal |
| Anthem / BCBS | 180 days (California: 365 days) | Availity portal (required enrollment) |
| Humana | 120 calendar days | Availity or mail |
| Medicare Part A/B | 120 days (Redetermination) | MAC — varies by state |
| Medicare Advantage | 60 days from denial notice | Plan-specific portal or mail |
| Medicaid | 90–120 days (varies by state) | State agency — varies |
UnitedHealthcare deadline warning: UHC's 65-calendar-day deadline is the most common source of missed appeals. Billing teams used to the standard 180-day window often underestimate how quickly UHC denials must be acted on. If you receive a UHC denial on a Friday, you have fewer than 9 weeks — including weekends and holidays — to submit your appeal.
Payer-Specific Appeal Tips
UnitedHealthcare (UHC)
UHC uses InterQual® clinical criteria — a proprietary decision support tool — for virtually all medical necessity reviews. Appeals that cite InterQual® criteria by name and align the patient's clinical picture to the specific criteria outperform generic letters by over 20 percentage points. Portal submission via UHCProvider.com is mandatory for most plan types. Request a peer-to-peer review simultaneously — UHC's overturn rate on peer-to-peer is 65–85%.
Aetna
Aetna uses MCG (Milliman Care Guidelines). Their appeal review process is generally more flexible than UHC's, but they require complete clinical documentation. For complex medical necessity denials, Aetna's peer-to-peer process is effective and typically scheduled within 5–7 business days of request.
Cigna
Cigna maintains its own proprietary clinical criteria. For behavioral health and specialty drug denials specifically, Cigna has a strong track record of overturning denials on internal appeal when adequate supporting documentation is submitted with the initial letter — meaning you should not hold documentation back expecting to escalate.
Anthem / Blue Cross Blue Shield
Anthem requires a claim payment dispute on file before filing a formal appeal — skipping this step will result in rejection of your appeal submission. Use the Availity portal, which requires enrollment. California BCBS plans have a 365-day appeal deadline — but do not use this as a reason to delay, as supporting documentation becomes harder to obtain over time.
Medicare
Medicare appeals follow a strict 5-level process: Redetermination → Reconsideration → ALJ Hearing → Medicare Appeals Council → Federal District Court. The first two levels (Redetermination and Reconsideration) have the highest overturn rates and lowest effort requirements. Always pursue at least these two levels before abandoning a claim.
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Internal vs. External Appeal: When to Escalate
If your internal appeal is denied, you have the right to external independent review. Under the Affordable Care Act, most commercial health plans must offer external review for clinical denials. The external reviewer is an independent, accredited organization — not the insurer — and its decision is binding on the payer.
External review overturn rates range from 40–60% depending on denial type and specialty. This means that even after losing an internal appeal, roughly half of externally reviewed denials are ultimately overturned. It is almost always worth escalating to external review for high-dollar clinical denials.
For Medicare beneficiaries, the equivalent process is a Qualified Independent Contractor (QIC) Reconsideration, followed by an Administrative Law Judge (ALJ) Hearing — which has historically high overturn rates for complex medical necessity cases.
How to Maximize Your Overturn Rate
Beyond writing a complete appeal letter, these practices consistently improve overturn rates across all payers:
- Request a peer-to-peer review simultaneously. A treating physician speaking directly to the payer's medical director overturns 65–85% of medical necessity denials. Request it the same day you submit the appeal letter — don't wait for an internal denial to escalate.
- Document failed conservative treatments with specifics. Payer criteria almost universally require evidence of failed lower-cost alternatives before approving higher-level services. Be specific: drug name, dose, dates, and documented failure — not "patient tried physical therapy."
- Track denial patterns by payer and code. Practices that track which denial codes recur most frequently for specific payers can address root causes upstream — changing documentation workflows, pre-authorization habits, or coding practices to prevent the same denials from reoccurring.
- Never miss a deadline. The single most preventable reason for permanent revenue loss is a missed appeal deadline. Use a system — a spreadsheet, a dedicated tool, anything — to log every denial date and calculate the appeal deadline the day the EOB arrives.