A denial letter can feel like a wall of jargon, but it is really just a short list of facts you need to extract. Your health plan calls a denial an “adverse benefit determination” — that exact phrase is your signal that formal appeal rights attach. Once you know the reason, the code, the deadline, and where to send your appeal, the rest is straightforward. Read your own letter carefully, because the details on it always control over any general guidance here.
What an “adverse benefit determination” is
An adverse benefit determination is any decision that reduces, delays, or refuses a benefit: a denied claim, a denied prior authorization, a reduced payment, or a service ruled not covered or not medically necessary. The law generally requires the plan to tell you why in writing and to explain how to appeal. If a notice does not state a clear reason, that is itself a problem you can raise on appeal.
The 6 things to extract
Work through your letter and the attached Explanation of Benefits (EOB) and pull out:
- The denial reason and code. The plan must state why. Common reasons: not medically necessary, experimental or investigational, out of network, no prior authorization, or not a covered benefit. You appeal to the reason actually stated — not what you assume it is.
- The CARC/RARC codes on the EOB. The EOB often lists Claim Adjustment Reason Codes and Remittance Advice Remark Codes that explain the dollar decision in coded form. They help you and your provider speak the plan’s language.
- Your member, claim, and group numbers. Every appeal must reference these so the plan can match it to your file.
- The appeal address (or fax/portal). Send your appeal exactly where the letter directs. Sending it to the wrong place can cost you time you do not have.
- The deadline. ACA-compliant plans generally give you 180 days from the denial notice to file an internal appeal. Your letter states the controlling date — confirm it there.
- Whether it is pre-service or post-service. Pre-service means the care has not happened yet (this affects decision timelines and whether you can request an expedited review). Post-service means you already received care and the bill was denied.
EOB vs denial letter
These are not the same document. The EOB summarizes how a claim was processed and shows the coded reasons and the amounts. The denial letter is the formal adverse-determination notice that triggers your appeal rights and states your deadline. Read both: the EOB tells you what the codes mean, and the letter tells you how and when to fight back. See /guides/read-your-denial-letter/ cross-references below for next steps.
What to do next
- Start your internal appeal within the stated deadline. See /guides/internal-appeal-letter/.
- Request the claim file if your coverage is through a self-funded employer plan (ERISA), so you can see the evidence the plan used. See /guides/request-claim-file-erisa/.
- Go expedited if the situation is urgent — when waiting could seriously jeopardize your health. See /guides/expedited-urgent-appeal/.
Notes. A denial is formally an “adverse benefit determination,” and ACA-compliant plans generally allow 180 days from the denial notice to file an internal appeal; the controlling deadline is always the one on your own letter — confirm it there. For timeframes see /guides/appeal-deadlines/, to choose your path see /guides/which-appeal-process/, and to draft your appeal see /guides/internal-appeal-letter/. This is general information, not legal, medical, or insurance advice.