Denial codes, explained by people who have coded
A denial code tells you a claim was adjusted. It rarely tells you what to do about it. These pages do: why you actually got each one, how to fix the one on your desk, and what would have stopped it before it left the building.
The prefix matters as much as the number. CO means the write-off is yours and you cannot bill the patient. PR means the money is the patient’s to pay and it is collectible. Reading a PR code as a denial is how practices give away revenue they were entitled to.
Stop the next one. Many diagnosis denials come from an Excludes1 pair, a header code or a missing seventh character — all visible before the claim goes out. Check a claim’s diagnosis codes free, no account needed.
CO — Contractual Obligation
The write-off is yours. You agreed to it in your contract with the payer, and you cannot bill the patient for it.
- CO-16The claim is missing information the payer needs, or something on it is inconsistent.
- CO-97The service is considered already paid for as part of another service on the same claim.
- CO-45Your charge was above the payer's allowed amount, and the difference is a contractual write-off.
- CO-22The payer believes another insurer should pay first.
- CO-197No prior authorization.
- CO-252The payer wants documentation before it will decide.
- CO-50The payer does not consider the service medically necessary for the diagnosis you submitted.
- CO-24The charge is covered under a capitation arrangement or managed care plan — meaning fee-for-service payment doesn't apply.
- CO-234This procedure is not paid separately — and the remark code next to it says why.
- CO-11The diagnosis does not match the procedure.
- CO-226The payer asked the billing provider for information and considers the answer missing, incomplete, or late.
- CO-236This procedure isn't compatible with another procedure billed on the same day, under the coding rules the payer applies.
- CO-253Sequestration.
- CO-4The procedure code is inconsistent with the modifier used, or a required modifier is missing.
- CO-18Duplicate claim or service.
- CO-96Non-covered charge.
- CO-59The payment was processed under multiple-procedure or concurrent-procedure rules.
- CO-131A claim-specific negotiated discount was applied — a rate agreed for this claim rather than by your standing contract.
- CO-29The claim was filed after the payer's deadline.
- CO-256Not payable per your managed care contract.
- CO-129The prior processing information on the claim looks wrong to the payer.
- CO-109This claim is not payable by this payer or contractor.
- CO-55The payer classifies the treatment as experimental, investigational, or unproven — outside what it considers established medicine, and therefore outside what it pays for.
- CO-8The procedure is inconsistent with the provider's type or specialty.
- CO-288No referral on file.
- CO-151The payer says the information submitted does not support this many services.
PR — Patient Responsibility
The amount is the patient's to pay: deductible, coinsurance, or copay. These are not denials, and they are collectible.
- PR-96Non-covered charge, and the patient owes it.
- PR-204The service is not covered under the patient's current benefit plan, and the balance is the patient's.
- PR-31The payer cannot match the patient to a member.
- PR-227The payer asked the patient for information and never got it, so the claim is denied to the patient.
- PR-119The benefit maximum has been reached — the plan's allowance for this service, this period, is used up, and further charges belong to the patient.
- PR-1The amount is applied to the patient's deductible.
- PR-242The services weren't provided by a network or primary-care provider, so the plan is paying less or nothing and assigning the difference to the patient.
- PR-200The expenses fall inside a lapse in coverage — the policy existed, but premiums weren't current when the service happened, so the plan is holding the patient responsible.
- PR-45The charge exceeds the fee schedule or allowed amount — and unlike CO-45, the PR prefix marks the excess as the patient's.
- PR-26The expenses predate the coverage — service rendered before the policy's effective date, so the plan says it hadn't started paying for this patient yet, and the bill is theirs.
- PR-2Coinsurance.
- PR-3Copay.
OA — Other Adjustment
An adjustment that is neither a contractual write-off nor patient responsibility.
RARC — Remark Code
A remark code adds detail to an adjustment. On a CO-16 it is the remark code that actually tells you what was missing.
- N130A remark code pointing you at the plan's benefit documents: the adjustment next to it is driven by something in the plan itself — a limit, a restriction, a condition of coverage.
- N19A remark code: the procedure is considered incidental to the primary procedure on the claim.
- N382A remark code: the patient identifier is missing, incomplete, or invalid.
- MA130Your claim is unprocessable: something on it is incomplete or invalid, and — this is the part that matters — it comes with no appeal rights, because in the payer's eyes no claim was ever properly filed.
Common questions
- What are denial codes?
- Denial codes are the standard codes a payer puts on a remittance advice to explain why a claim was reduced, adjusted, or not paid. They come in two kinds: claim adjustment reason codes (CARC codes), which say what the adjustment was, and remittance advice remark codes (RARC codes), which add the detail. The group prefix matters as much as the number: CO means the write-off is yours contractually, while PR means the amount is the patient's to pay.
- What is the most common denial code?
- CO-16 is the most common. It means the claim is missing information or something on it is inconsistent, and on its own it tells you very little — the useful detail is in the remark codes on the same remittance line.
Most coding-side denials are visible before the claim leaves: paste the diagnosis codes into the free claim scrubber and it will flag the conflicts. The denial management page explains how the paid workspace runs those checks on every claim, and the ICD-10-CM lookup shows the coding notes behind any diagnosis code on the remittance.
Every explanation on these pages is our own. The official descriptions of the claim adjustment reason codes are published and copyrighted by X12, and we do not reproduce them — read the official list at X12. Reference information for professional coders and billers; not billing or legal advice.