Denial codes
What the code on your remittance actually means
Every denial arrives as a code and a sentence of payer shorthand. These guides translate the codes that cost independent practices the most, and say plainly which ones are worth your time.
- CO-197CO-197 denial: prior authorization absentThe payer says the service needed prior authorization and it did not have one on file when the claim was processed.Usually worth appealing
- CO-16CO-16 denial: claim lacks informationSomething on the claim is missing or malformed. CO-16 almost never travels alone — a RARC alongside it tells you what.Usually worth appealing
- CO-29CO-29 denial: timely filing limit expiredThe payer says the claim arrived after its filing deadline — so it will not consider the claim at all.Sometimes worth appealing
- CO-45CO-45: charge exceeds fee scheduleYour billed charge was higher than the contracted rate. The difference is a normal contractual write-off, not a denial.Rarely worth appealing
- CO-50CO-50 denial: not deemed medically necessaryThe payer decided the service was not medically necessary under its coverage policy for this diagnosis and setting.Usually worth appealing
- CO-97CO-97 denial: service already included in another paymentThe payer treated this service as already paid for as part of another service on the claim.Sometimes worth appealing
- CO-18CO-18 denial: exact duplicate claimThe payer believes it has already received this exact claim, so it will not process it a second time.Sometimes worth appealing
- CO-22CO-22 denial: another payer is primaryThe payer thinks someone else is primary and wants that payer to process the claim first.Sometimes worth appealing
- CO-27CO-27 denial: coverage terminated before the serviceThe payer says the patient's coverage had already ended on the date of service.Sometimes worth appealing
- CO-96CO-96 denial: non-covered chargesThe payer says the plan does not cover this service at all — a benefit decision, not a clinical one.Sometimes worth appealing
- CO-109CO-109 denial: claim sent to the wrong payerThe claim went to the wrong payer. This one is a routing problem, not a denial to argue with.Rarely worth appealing
- CO-151CO-151 denial: too many services billedThe payer accepts the service but not how many of them, or how often they were provided.Usually worth appealing
- CO-B7CO-B7 denial: provider not eligible on the date of serviceThe payer says the rendering provider was not enrolled, credentialed, or eligible on the date of service.Usually worth appealing
- CO-4CO-4 denial: modifier inconsistent or missingThe payer says the modifier and the procedure on the claim do not agree, or a required one is absent.Sometimes worth appealing
- CO-11CO-11 denial: diagnosis inconsistent with the procedureThe payer says the diagnosis on the claim does not support the procedure that was billed.Sometimes worth appealing
- PR-1PR-1: deductible amount — and why it is not a denialNot a denial at all. The claim was covered, and this portion applies to the patient's deductible.Rarely worth appealing
- PR-204PR-204: not covered under the patient's benefit planThe plan does not cover this item, and the payer is assigning the cost to the patient.Sometimes worth appealing
CO, PR, OA, PI — the group code decides who pays
The two letters in front of the number matter more than the number. They determine whether the amount is your write-off or the patient’s bill.
- COContractual Obligation
- The amount is written off under your contract with the payer. You cannot bill the patient for it.
- PRPatient Responsibility
- The amount moves to the patient — deductible, copay, coinsurance, or a non-covered service they agreed to.
- OAOther Adjustment
- Neither a contractual write-off nor patient responsibility. Often used when another payer is primary.
- PIPayer Initiated Reduction
- The payer decided the amount is not payable and, unlike CO, does not consider it a contractual write-off.
Stop looking codes up. Appeal them.
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