REFERENCE

Insurance Denial Codes Explained

Plain-English explanations of the most common insurance denial and adjustment codes. Click any code to see what it means, what you owe, and exactly what to do next.

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Contractual Adjustments (CO codes)

CO-4Missing or incorrect modifierYour claim was missing a code that tells the insurer more detail about how or where a service was performed. Without it, the claim cannot be processed.CO-11Diagnosis does not support the procedureThe insurer says the diagnosis code on your claim does not justify the procedure that was billed. This is often a coding mismatch, not a clinical judgment.CO-15Prior authorization missing or invalidThe insurer required pre-approval for this service before it was performed, and that approval was either not obtained or is not showing correctly on the claim.High when clinical documentation is strong CO-16Missing information or submission errorThe claim is incomplete. A required field such as patient ID, provider NPI, or supporting documentation is missing or incorrect.Very high when corrected and resubmitted CO-18Duplicate claimThe insurer has already received and processed this claim. A second submission was flagged as a duplicate.CO-19Claim denied because this is a work-related injuryThe insurer believes your injury or condition is related to your job and should be covered by workers compensation, not your health plan.Moderate when documentation is clear CO-22Another payer is primaryThe insurer says a different insurance plan should pay this claim first. Your health plan considers itself secondary.CO-23Claim denied because payment made to patientThe insurer sent payment directly to you instead of your provider. Your provider may be billing you again for a balance that was already paid.CO-26Expenses incurred prior to coverageThe service was performed before your insurance coverage started. The insurer will not cover services that occurred before your effective date.Low unless enrollment date is incorrect CO-27Expenses incurred after coverage endedYour coverage had ended by the time this service was performed. The insurer will not pay for services after your termination date.Low unless coverage termination was in error CO-29Claim filed after the deadlineYour provider submitted the claim after the insurer filing deadline. Most insurers have strict windows, typically 90 to 365 days from the date of service.Low -- deadlines are strictly enforced CO-31Patient cannot be identified as insuredThe insurer cannot match the patient on this claim to an active member in their system. This is usually a data entry error.Very high when corrected CO-45Charges exceed the allowed amountYour provider billed more than what your insurer has agreed to pay for this service. If your provider is in-network, you cannot be billed for the difference.CO-50Medical necessity deniedThe insurer decided the service was not medically necessary based on their coverage criteria. This is one of the most common and most frequently overturned denials.High -- approximately 44% of internal appeals succeed industry-wide CO-51Not medically necessary -- quantity exceeds plan limitsThe insurer approved this service but says you received more units or visits than your plan covers. The excess amount is being denied.Moderate with strong clinical documentation CO-55Procedure code billed is inconsistent with place of serviceThe code your provider used indicates a service that does not match where the service was performed. For example, a hospital code billed for an office visit.Very high when corrected CO-57Revenue code and procedure code do not matchThe billing codes on your claim are internally inconsistent. The facility revenue code does not align with the procedure code used.Very high when corrected CO-58Treatment not authorized by planThis specific treatment was not authorized by your plan. Different from a prior authorization issue -- this means the treatment itself falls outside covered benefits.Moderate depending on plan type and state CO-59Processed based on multiple physician fee scheduleYour claim was adjusted because it falls under a special payment arrangement. This is typically an informational code, not a denial.CO-96Non-covered chargeThis service or item is not covered under your health plan. This is one of the broadest denial codes and can cover a wide range of excluded services.Low to moderate depending on service type CO-97Service bundled into another paymentThe insurer says this service is already included in the payment for a different service billed at the same time. You cannot be paid separately for it.CO-109Wrong payer billedThe claim was sent to the wrong insurance company. This is a billing error.CO-119Benefit maximum for this time period has been reachedYou have used up your plan benefit for this type of service for the year or coverage period. No additional claims for this service will be paid until the benefit resets.Low unless limit calculation is wrong CO-125Submission does not comply with payer policyYour claim did not follow the insurer required format or submission rules. This is an administrative denial, not a clinical one.Very high when corrected CO-129Prior processing information appears incorrectThe insurer found inconsistencies in how a previous related claim was processed, affecting this claim.CO-131Claim specific negotiated discountA discount has been applied to this claim based on a negotiated agreement between your provider and insurer. This is informational and typically not a denial.CO-133Outsourced serviceThis service was performed by a provider that operates outside your plan network or through a third-party arrangement.Moderate with No Surprises Act documentation CO-146Diagnosis was invalid for date of serviceThe diagnosis code used on your claim was not valid or had not been adopted yet on the date your service was performed.Very high when corrected CO-149Lifetime benefit maximum reachedYou have reached the maximum benefit your plan will pay over your lifetime for this type of service. Most lifetime limits were eliminated by the ACA for essential health benefits.High for ACA-covered essential health benefits CO-167Diagnosis is not coveredYour insurer does not cover services for this specific diagnosis under your plan. This may be an exclusion in your plan documents.Low to moderate depending on diagnosis and state CO-170Payment denied when performed by a provider of the same specialtyTwo providers with the same specialty billed for the same service on the same day. Insurers typically pay only one provider per specialty per day.Moderate with documentation CO-173No authorization obtained for services rendered to this patientA specific type of service required your insurer approval before it was performed, and your provider did not get it.Moderate for emergency situations CO-176Patient has not met the required eligibility requirementsThe insurer determined you do not meet the plan eligibility criteria for this service. This could be age, enrollment status, or other requirements.Moderate with documentation CO-185Denied because the procedure or treatment is deemed experimentalYour insurer considers the treatment or procedure experimental or investigational and therefore not covered under your plan.Moderate with strong clinical literature CO-197Precertification or authorization absentYour plan required advance approval for this service and it was not obtained before the service was performed.Moderate for urgent or emergency situations CO-204Service or supply not covered by the planThis specific service or supply is listed as excluded in your plan. It is a broader exclusion than CO-96.Low to moderate CO-236This procedure or procedure or modifier code combination is not compatibleThe combination of procedure codes or modifiers used on your claim cannot be billed together according to standard coding rules.Very high when corrected

Patient Responsibility (PR codes)

PR-1Deductible appliesYou have not yet met your annual deductible. You are responsible for this amount until your deductible is satisfied. This is not a denial -- it is how your plan works.PR-2Coinsurance appliesYou are responsible for your share of the cost after the deductible is met. Your plan covers a percentage and you owe the rest. This is not a denial.PR-3Copay appliesYou owe a fixed copay for this service. This is not a denial -- it is your plan standard cost-sharing.PR-26Expenses incurred prior to coverageYou are responsible for this charge because coverage was not active when the service was performed.Low unless coverage date is wrong PR-27Expenses incurred after coverage terminatedYour coverage had ended when this service was performed. You are responsible for the amount.Low unless termination was in error PR-96Non-covered charge -- patient responsibilityThis service is not covered by your plan and you are responsible for the full amount. This is the patient responsibility version of CO-96.Low to moderate PR-119Benefit maximum for this time period has been reached -- patient responsibilityYou have exhausted your benefit limit for this type of service. The patient responsibility version means you owe the amount.Low unless limit calculation is wrong

Other Adjustments and Remark Codes

OA-18Duplicate claim -- other adjustmentA duplicate claim adjustment has been applied. This is the other adjustment version of CO-18.OA-23Payment adjusted because charges have been paid by another payerAnother insurer already paid this claim. The adjustment reflects coordination of benefits between your two insurance plans.OA-109Claim not covered by this payer -- resubmit to correct payerThis claim does not belong with this insurer. It should be sent to a different payer.N1Alert: you may appeal this decisionThis remark code is informational. It tells you that you have the right to appeal this denial or adjustment.N130Consult your provider for additional informationYour insurer is directing you to your provider for more information about this claim or denial. This is typically an informational remark code.N517Resubmit with applicable service datesThe claim is missing or has incorrect service dates. The insurer cannot process it without accurate date information.Very high when corrected MA01Alert: you may be billed for this amountThis Medicare remark code tells you that you may be held financially responsible for this amount. It is informational and does not automatically mean you owe it.MA04Secondary payment cannot be considered without the identity of or payment information from the primary payerMedicare needs information about your primary insurer before processing this as a secondary payer. This is a coordination of benefits issue.Very high when documentation provided

Payer-Specific Codes

610Charges exceed allowable amount -- payer-specificThis payer-specific code is used by some insurers including Wellmark Blue Cross Blue Shield to indicate that billed charges exceed the allowable rate. If your provider is in-network, you are not responsible for the difference.

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