Every denial on your EOB comes with a standardized CARC code. The codes are cryptic by design — but each one has a specific meaning, a responsible party, and a fix. Find yours below.
The insurer says your treatment wasn't needed. They reviewed the claim against their own clinical criteria, not your doctor's judgment, and concluded the service wasn't warranted for your condition. This is the most common clinical denial, and one of the most frequently overturned on appeal when your doctor backs you up.
The insurer classifies this treatment as experimental: insufficient evidence, in their view, to count as established medical practice. This shows up on genuinely novel treatments, but also on off-label uses of FDA-approved drugs and on newer techniques the insurer simply hasn't added to policy yet. External review is unusually effective here when the clinical evidence is strong.
A close cousin of the experimental denial: the insurer says the treatment hasn't been proven to work. The dispute is about evidence, which means the appeal is about evidence: published studies, clinical guidelines, and your doctor's documentation of why this treatment fits your case.
The insurer agrees you needed care. They just don't think you needed this much. A Level 4 office visit they think should have been a Level 3, an inpatient stay they think should have been outpatient. Very often the care was appropriate and the documentation submitted with the claim simply didn't show it.
The insurer required pre-approval for this service and none was on file when the claim processed. In most cases, obtaining authorization was the provider's job. If they failed to do it, that's their problem, not yours. Emergency services are exempt from prior authorization entirely.
The claim needed an authorization number and either didn't include one, or included one that's wrong: a typo, an expired authorization, or a number issued for a different provider or service. If authorization was actually obtained, this is one of the fastest denials to fix: add the right number, resubmit, done.
Authorization existed, but the care went beyond it: more therapy sessions than approved, a longer hospital stay, an extra procedure during surgery. Managing an ongoing authorization (extensions, concurrent review) is the provider's responsibility, and in most scenarios they should be appealing rather than billing you.
Something required was missing from the claim or entered incorrectly: a provider ID, a date of birth, a place-of-service code, a diagnosis code. This is the most general administrative denial there is, and the accompanying remark code (RARC) tells you exactly what was missing. It says nothing about whether your care was covered. The paperwork just failed.
The insurer says they already received and processed this exact claim, and this is a second copy. Usually that's true: a billing system submitted twice, or a corrected claim wasn't marked as a correction. The question that matters: was the original claim actually paid?
The provider submitted the claim after the insurer's filing deadline. This is the provider's error: meeting filing deadlines is a basic contractual obligation between them and the insurer. You should not owe a dime because their billing office missed a date.
The claim has a modifier problem. Modifiers are two-character add-ons to procedure codes that carry details like which side of the body was treated or whether a procedure was distinct from another one billed the same day. A missing or wrong modifier is a provider coding error. Nothing about your care was judged.
The diagnosis code (what's wrong with you) doesn't line up with the procedure code (what was done about it) according to the insurer's coding logic. Nine times out of ten this is a provider coding issue: a non-specific diagnosis code, or a diagnosis entered on the wrong line of a multi-service claim.
The insurer says these charges aren't covered under your plan. On its own this code is vague. The accompanying remark code (RARC) carries the real reason. Sometimes the exclusion is genuine. Often enough, the service was misclassified (a medically necessary procedure coded as cosmetic, for example), and that's appealable.
Your plan doesn't cover this specific service, piece of equipment, or drug. Because the group code is PR, the insurer is putting the amount on you. Before you pay, confirm the exclusion is real: benefit-plan denials are frequently the product of a wrong code, an outdated formulary entry, or a coverage category the claim landed in by mistake.
The insurer says you weren't covered on the date of service: your coverage had ended. Sometimes that's true (job change, missed premium, aging off a parent's plan). But insurer enrollment records are wrong often enough that this denial deserves verification, especially around job transitions, COBRA elections, and plan-year changes.
The insurer says treatment for this particular condition is excluded from your coverage. The issue is not that the treatment was unnecessary but that the diagnosis itself falls outside the plan. Check this one carefully: mental health and substance-use exclusions can violate federal parity requirements, and a miscoded diagnosis can land a covered condition in an excluded category.
The provider charged more than the insurer allows for this service. For an in-network provider, this is the routine contractual discount: the provider agreed to accept the insurer's rate, and the CO-45 amount is written off. It only becomes your problem when the provider is out-of-network, where the difference can turn into balance billing.
The insurer says this service is already included in what they paid for another service: they're treating the two as one bundle rather than separate charges. Often this is correct (NCCI bundling rules exist for exactly this reason). But when the two services were genuinely distinct (different sites, different sessions, different purposes), the claim needs a modifier and a second look.
The insurer paid less for a second (or third) procedure performed in the same session, on the theory that doing procedures together is more efficient than doing them separately. Standard multiple-procedure reductions are legitimate. The problem case is when genuinely distinct procedures (different sites, different purposes) get swept into the reduction because a modifier was missing.