A denial is not the end. You have legally protected rights to appeal — and appeal wins are common. This guide walks through every level of the appeal process, from your first phone call to the state insurance commissioner.
Every insurance denial generates an Explanation of Benefits (EOB) — a document your insurer is required to send that explains how a claim was processed and why it was denied (or partially denied). The EOB is the foundation of your appeal. Without understanding exactly why the claim was denied, you can't build an effective appeal.
The EOB will contain a denial reason code — either an ANSI X12 code (like CO-97 or PR-2) or a plain-English description. Locate this reason before doing anything else.
Log in to your insurer's member portal — EOBs are always available there. You can also call the member services number on your insurance card and ask for the EOB for a specific claim date. Your provider may also have received an Explanation of Payment (EOP) that mirrors your EOB.
These are the denial and adjustment reason codes you're most likely to encounter. Knowing what the code means tells you which documents to gather for your appeal.
| Code | Meaning | What to Do |
|---|---|---|
| CO-4 | Service requires prior authorization / referral not obtained | Request retro-authorization if emergency or urgent; appeal citing medical necessity if not obtained due to insurer error |
| CO-22 | Coordination of benefits issue — another insurer should be primary | Verify COB order with HR or both insurers; resubmit with correct primary/secondary designation |
| CO-50 | Non-covered service — not medically necessary as billed | Obtain a letter of medical necessity from your physician; appeal citing clinical guidelines |
| CO-97 | Benefit for this service included in another service already paid | Often a bundling issue — request itemization; if services were distinct, appeal with documentation of separate encounters |
| CO-109 | Claim not covered by this payer — patient may be covered by another plan | Verify your insurance is current; if there's been a plan change, confirm effective dates and resubmit |
| PR-1 | Deductible amount — your responsibility | Verify deductible correctly applied; check if deductible was already met through prior claims |
| PR-2 | Co-insurance amount — your responsibility | Verify co-insurance percentage matches your plan documents; check for network status error |
| PR-3 | Co-pay amount — your responsibility | Verify co-pay matches your plan; confirm provider's network status |
| PR-96 | Non-covered charge(s) | Request the specific exclusion in your plan language; if not clearly excluded, appeal citing plan ambiguity |
| OA-18 | Duplicate claim or service submitted | Verify only one claim was submitted; if so, request manual review of both claims |
| OA-23 | Insufficient information / documentation | Provide missing documentation (operative notes, progress notes, referral letter) and resubmit |
An internal appeal is your first formal challenge — submitted directly to your insurance company. Under the ACA (for ACA-compliant plans) and the Employee Retirement Income Security Act (for employer plans), you have the right to a full and fair internal review of any adverse benefit determination.
Call member services and request the "complete claim file" for the denied claim — all documents, records, and guidelines used in the denial decision. The insurer is legally required to provide these within 30 days of your request. Your appeal deadline is on your EOB — typically 180 days from the denial date.
For medical necessity denials (CO-50 and similar), a detailed letter from your treating physician is the single most important document. It should explain your diagnosis, why this specific treatment was necessary and not merely convenient, what alternatives were considered and why they weren't appropriate, and any relevant clinical guidelines or peer-reviewed literature supporting the treatment.
Address the specific denial reason directly. Don't just say "I disagree" — explain precisely why the denial is incorrect, citing your plan documents, the medical necessity letter, clinical guidelines, and any relevant case law or regulations. Keep it concise and evidence-focused.
Send your appeal letter, supporting documentation, and a copy of your EOB by certified mail with return receipt. Keep a full copy for yourself. Note the claim number, appeal date, and tracking number.
If you receive no response within 60 days (or 30 for pre-service), call and document the delay. A failure to respond timely may itself be an appealable adverse determination or grounds for external review.
Some insurers offer a voluntary second-level internal appeal after the first is denied. While not required by federal law, some states mandate it. Check your plan documents or call member services. A second-level appeal reviewed by a medical director (rather than a claims adjuster) often has a higher success rate — particularly for complex medical necessity denials.
If your internal appeal is denied (or if the insurer fails to respond within the required timeframe), you have the right to an independent external review — a review by an Independent Review Organization (IRO) that is completely unaffiliated with your insurer. The insurer must abide by the IRO's decision.
External review is free to you. The insurer pays the IRO's fee. The IRO's decision is legally binding on the insurer.
The process for requesting external review will be in your internal appeal denial letter. Some states have their own external review process; others use the federal process. Your insurer must tell you which applies.
The IRO will review your medical records, the insurer's guidelines, and any clinical evidence you submit. Add any peer-reviewed studies, specialist opinions, or professional society guidelines that support coverage for your treatment.
The assigned IRO will contact you with instructions. Provide your full case in a clear, organized format: EOB, denial letter, medical records, physician letters, and any supporting clinical literature.
If the IRO decides in your favor, notify your insurer in writing and request immediate processing of the claim. If the IRO denies it, you still have state insurance commissioner and, in some cases, legal options.
Your state insurance commissioner regulates insurance companies doing business in your state. Filing a complaint with the commissioner is free and often remarkably effective — insurers respond quickly to regulatory complaints because the commissioner can impose fines, require corrective action, and audit the insurer's claims practices.
The state commissioner is particularly effective for: benefit exclusion disputes that don't qualify for external review, network adequacy complaints (you couldn't find an in-network provider for a needed service), balance billing violations, and failure to follow state-mandated timelines.
Search "[your state] insurance commissioner file a complaint" or visit naic.org for a directory of all state commissioners with direct links to their complaint portals.
Include your EOB, the denial letter, your appeal and the insurer's response, and a brief, factual summary of the dispute. Stick to the facts; avoid emotional language. The commissioner's staff reviews these and determines regulatory violations.
Most state commissioners require the insurer to respond within 14–21 days. The commissioner then reviews the response and may intervene directly. Many disputes are resolved at this stage — insurers know that repeated complaints trigger audits of their entire claims operation.
State insurance commissioners regulate fully-insured plans (individual and small group plans purchased through an employer or an exchange). They do not have jurisdiction over self-funded employer plans — those are governed by ERISA (see Stage 4 below). If you're unsure which type of plan you have, ask your HR department: "Is our health plan fully insured or self-funded (self-insured)?"
The Employee Retirement Income Security Act (ERISA) governs most employer-sponsored health plans in the U.S. — specifically self-funded plans where the employer bears the insurance risk. ERISA creates both specific appeal rights and, ultimately, the right to sue in federal court.
Under ERISA, you must exhaust all internal appeals before filing suit in federal court. Your plan documents define the internal appeal process. Failure to exhaust is a procedural bar to the federal lawsuit — so follow the internal appeal process precisely, even if you expect it to fail.
Everything you submit during the internal appeal process becomes part of the "administrative record" — the only evidence a federal court can consider when reviewing your case. Submit everything relevant during the appeal, including all medical records, physician letters, clinical guidelines, and legal arguments. You cannot add new evidence in court.
Request the complete plan documents (SPD) and the full claim file in writing. Under ERISA Section 104, the plan administrator must provide these. Compare the denial to the plan language — a common winning argument is that the denial was arbitrary and capricious based on the plan's own definitions.
ERISA litigation is specialized. Many ERISA attorneys take cases on contingency for large denials. Under ERISA, if you win, the plan pays your attorney's fees — which creates a real incentive for attorneys to take these cases. Find one at healthinsuranceappeal.com or through your state bar's referral service.
When your health or life is at risk, you cannot wait 60 days for an internal appeal decision. Both the ACA and ERISA provide expedited appeal timelines for urgent care situations.
If a standard appeal timeline would seriously jeopardize your health, life, or ability to regain maximum function, you may request an expedited appeal. The insurer must respond within 72 hours. Request this verbally AND in writing simultaneously. Mark all communications "URGENT — EXPEDITED APPEAL."
You can request expedited external review at the same time as your internal appeal if the urgency of your situation warrants it. You do not have to wait for the internal appeal to be decided. The IRO must respond within 72 hours. This is one of the exceptions to the rule requiring exhaustion of internal appeals first.
| Stage | Your Deadline to File | Insurer/IRO Response Deadline |
|---|---|---|
| Internal Appeal (post-service) | 180 days from EOB | 60 days |
| Internal Appeal (pre-service) | Varies — check plan docs | 30 days |
| Expedited Internal Appeal | As soon as possible | 72 hours |
| External Review Request | ~4 months (60 business days) from internal denial | 45 days (standard) |
| Expedited External Review | Same time as expedited internal appeal | 72 hours |
| State Commissioner Complaint | Varies by state; typically no hard deadline | 14–30 days (insurer must respond to commissioner) |
| ERISA Federal Lawsuit | After all internal appeals exhausted; typically 3–6 year statute of limitations | Court-ordered |
The deadlines above are federal minimums for ACA-compliant and ERISA plans. Your specific plan may have shorter deadlines. The deadline for your plan is always stated on the denial letter / EOB. Never miss the appeal deadline — it can permanently forfeit your right to contest the denial.
Many insurance denials stem from billing code errors, not actual coverage gaps. Upload your bill and we'll identify the specific coding issues — plus generate a dispute letter. $49 flat fee.