Adverse Benefit Determination
The formal legal term for a claim denial, reduction, or termination of benefits. ERISA plans are required to describe their decisions using this language. When a letter says "adverse determination," it means you have the right to appeal.
Ambulatory Service
Outpatient care — treatment that does not require an overnight hospital stay. Denials often cite whether care could have been delivered as ambulatory rather than inpatient.
Appeal Deadline
The maximum number of days you have to file an appeal, counted from the date on the denial letter. For ACA-compliant plans this is typically 180 days, but non-ACA and ERISA plans can be shorter. A missed deadline usually extinguishes your right to appeal — always check your specific plan.
Claim Number
The unique ID your insurer assigns to each claim. You need it on every letter, every phone call, and every appeal. It is usually near the top of your EOB.
COBRA
Federal law letting you keep your employer's health plan (at full cost) for a limited time after leaving a job. Denials on COBRA coverage follow the same appeal rules as the underlying employer plan (usually ERISA).
Coinsurance
The percentage of a covered claim you pay after meeting your deductible (e.g. 20%). Coinsurance disputes are usually math errors on the insurer's side, and the EOB breakdown is your proof.
Denial Code (CARC / RARC)
A standardized code on your EOB explaining why a claim was denied (Claim Adjustment Reason Code) or remarked on (Remittance Advice Remark Code). Every code maps to a specific reason — look it up to know exactly what argument your appeal needs to make.
EOB — Explanation of Benefits
A statement from your insurer showing what was billed, what they paid, and what you owe. An EOB is not a bill. It's the primary evidence you'll cite in an appeal — keep every one you receive.
ERISA
The Employee Retirement Income Security Act of 1974. The federal statute governing most employer-sponsored health plans. ERISA plans have parallel appeal protections to ACA plans but different deadlines and remedies — and a missed ERISA appeal deadline can prevent a future lawsuit.
Experimental / Investigational
A denial reason claiming the treatment is still being studied and therefore isn't covered. Frequently overturned on appeal when the patient submits FDA approval status, peer-reviewed studies, and clinical practice guidelines (e.g. from NCCN, AHA, or relevant specialty societies).
External Review
The second appeal stage, decided by an independent third party (the IRO) rather than your insurer. External-review decisions are binding: if the IRO sides with you, the insurer must pay. You must usually exhaust internal appeals first.
Formulary
The list of prescription drugs covered by your plan, usually organized in tiers with different cost-sharing. A "non-formulary" denial can be appealed with a letter of medical necessity explaining why the covered alternatives won't work.
Internal Appeal
The first appeal stage, decided by your insurer. Federal law requires the review be done by someone not involved in the original denial and, for clinical denials, by a doctor in the same specialty. Most overturns happen here.
IRO — Independent Review Organization
The third-party entity that decides external-review appeals. IROs are credentialed and cannot be affiliated with your insurer. Their decisions are binding on the insurer.
Letter of Medical Necessity
A letter from your treating doctor explaining, in clinical terms, why the denied service is necessary for your specific condition. The single most important piece of evidence in a medical-necessity appeal.
Medical Necessity
A standard insurers use to decide whether care is covered. It is a judgment call that can be successfully challenged. "Not medically necessary" is one of the most commonly overturned denial reasons when the patient supplies clinical notes, evidence-based guidelines, and a letter from the treating physician.
In-Network / Out-of-Network
Providers who have contracted rates with your plan (in-network) vs. those who haven't (out-of-network). Out-of-network denials can sometimes be overturned when no in-network specialist was available, under the federal No Surprises Act, or when the out-of-network care was an emergency.
No Surprises Act
A 2022 federal law protecting patients from surprise out-of-network billing for emergency services and for care at in-network facilities. If an out-of-network bill should have been covered in-network under this law, cite it by name in your appeal.
Peer-to-Peer Review
A phone conversation between your treating doctor and the insurer's reviewing doctor. Not technically an appeal, but often resolves denials before a formal appeal is filed. Ask your provider to request one when a clinical denial comes in.
Pre-existing Condition
A health issue that existed before a new insurance policy started. Under the ACA, insurers generally cannot deny coverage or claims based on pre-existing conditions in individual and small-group plans. Older grandfathered plans and short-term plans may still do so.
Retrospective Review
When the insurer reviews a claim after services were rendered. Common pattern: a service was covered, then retrospectively denied. Appeals in this scenario should document that the care was delivered reasonably under the information available at the time.
Self-Funded (Self-Insured) Plan
An employer plan where the employer pays claims directly (often using an insurer to administer). Self-funded plans are governed by ERISA rather than state insurance law, which affects your appeal rights and any follow-up litigation. The name of the insurer on your card doesn't tell you whether the plan is self-funded — check your plan documents.
Step Therapy
A rule requiring you to try cheaper drugs first before the plan covers a more expensive one, even if your doctor prescribes the expensive one initially. Step-therapy denials can be appealed with documentation showing the cheaper alternatives failed, caused intolerable side effects, or are medically contraindicated.
Usual, Customary & Reasonable (UCR)
The amount an insurer decides is a fair price for a service based on geography and provider type. UCR disputes can be challenged with comparable-rate data and billed-charge studies.
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