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 thinks you got this service too many times or too often: more physical therapy sessions than their guidelines suggest, imaging repeated sooner than their schedule expects. Their guideline is a population average. Your appeal is the documented reasons your case needed more.
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.
The insurer is saying they already said no: authorization was requested before the service and denied, and the service happened anyway. This is different from forgetting to ask (CO-197). The paper trail matters here, because what the insurer calls a denial was sometimes a request for more information that nobody followed up on.
Your plan required a referral (typically from your primary care provider) before you saw this specialist, and no referral was on file when the claim processed. Often the referral exists and simply never made it onto the claim, which makes this one of the more fixable denials on the list.
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.
Two codes on the claim disagree with each other: the revenue code (which department or service category the hospital billed under) doesn't match the procedure code (what was actually done). This is a clerical inconsistency in the provider's billing, and it says nothing about your coverage or your care.
The insurer couldn't match the claim to you. A transposed digit in the member ID, an outdated card on file, a name that doesn't match their records. Trivial cause, expensive consequence: claims denied this way often come back to you billed at full price as if you were uninsured, for a typo that was never yours.
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.
You've hit a coverage cap for this specific benefit: an annual visit limit (say, 20 physical therapy visits), a day limit, or a dollar cap for a category of care. Sometimes the cap is real plan design. But the ACA prohibits annual and lifetime dollar limits on essential health benefits, so a dollar cap on essential care deserves scrutiny before you accept it.
The insurer says the service happened before your coverage started. Around job changes and plan-year transitions this is sometimes true and often wrong: effective dates get entered incorrectly, and claims get sent to the new insurer when they belonged with the old one.
The insurer classified the service as routine or preventive and says the plan doesn't cover it. Read that twice, because the ACA requires most plans to cover a long list of preventive services at no cost to you. This denial often means a coding mismatch: a preventive visit coded as diagnostic, a covered screening billed under the wrong code, or a legitimate charge for the diagnostic part of a visit that started preventive.
The insurer denied this as a pre-existing condition. For most health coverage in America, that's a reason from a bygone era: the ACA banned pre-existing condition exclusions in ACA-compliant plans. Seeing this code on a marketplace or employer health plan claim should raise your eyebrows. It survives legitimately mainly in plans the ACA doesn't reach: short-term limited-duration plans, some grandfathered plans, and certain non-medical coverage like some disability or supplemental policies.
The insurer processed this as care from outside your plan's network, or from someone other than your designated primary care provider. On HMO-style plans that can mean no coverage at all. Before accepting it, verify the network status yourself: provider directories are wrong often enough that the industry has a name for it (phantom networks), and the No Surprises Act protects you in several out-of-network scenarios you didn't choose.
The insurer believes you have other health insurance that should pay first: a spouse's plan, a parent's plan, Medicare. The treatment isn't being questioned at all; the billing order is. COB denials are almost always fixable, because the only thing wrong is which insurer got the claim first.
You have two insurance plans, and this code shows how the first plan's payment affected what the second plan pays. OA-23 is coordination of benefits working as designed, not an error. The number it carries should match what your primary plan actually paid or adjusted, and that match is the thing to verify.
The claim went to the wrong insurance company. Not denied on the merits; just delivered to the wrong address. Common around plan switches, dual coverage, Medicare transitions, and injuries that belong with workers' comp or auto insurance instead of health insurance.
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.
Two procedures billed for the same day aren't allowed together under the National Correct Coding Initiative, the federal rulebook of code combinations. Usually one code already includes the other, so this denial is the system catching a billing conflict, not judging your care. The provider either billed incorrectly or needs to justify why the procedures were genuinely separate.
This is not a denial. The amount is being applied to your annual deductible, the amount you pay out of pocket before your insurance starts paying its share. Seeing PR-1 is normal plan operation. What deserves your attention is the amount: deductibles get misapplied often enough that verifying the number against your own running total is worth two minutes every time.
This is your coinsurance: the percentage of the allowed amount you pay after your deductible is met. Common rates run 10 to 20 percent in-network and 30 to 50 percent out-of-network. PR-2 itself is normal. The two things that go wrong with it are the wrong percentage being applied, and coinsurance continuing to accrue after you've hit your out-of-pocket maximum.
Your copay: the fixed dollar amount you pay for a type of visit. Normal plan operation, and usually correct. The errors worth catching are a specialist copay applied to a primary care visit, a copay charged on a preventive service that should be free under the ACA, and copays continuing after your out-of-pocket maximum is met.