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Claim denial codes, explained in plain English

Every common adjustment reason code (CARC) and remark code (RARC) on an EOB or 835, what it really means, how to fix it and whether it is worth appealing.

Who owes the money: group codes

CO Contractual obligation. The provider must write this off. The patient cannot be billed for it.

PR Patient responsibility. The patient owes this amount (deductible, coinsurance, copay or a non-covered service the patient agreed to pay).

OA Other adjustment. Neither CO nor PR applies, often used for coordination of benefits or prior payments.

PI Payer initiated reduction. The payer reduced the payment and believes the patient should not be billed.

CR Correction or reversal. A correction to an earlier payment, usually followed by a corrected payment.

Patient balance

PR-1Deductible PR-2Coinsurance PR-3Copay

Contract adjustment

CO-45Charge exceeds fee schedule CO-253Sequestration

Eligibility / coverage

CO-24Covered by managed care plan CO-26Service before coverage started CO-27Service after coverage ended CO-31Patient not identified as insured CO-109Not covered by this payer CO-B9Patient in hospice CO-B11Transferred to proper payer

Prior authorization

CO-15Authorization number missing or invalid CO-39Authorization denied CO-197Precertification / authorization absent CO-198Authorization exceeded CO-243Services not authorized by network provider

Coding error

CO-4Modifier inconsistent with procedure CO-5Place of service inconsistent CO-6Procedure inconsistent with age CO-7Procedure inconsistent with gender CO-9Diagnosis inconsistent with age CO-11Diagnosis does not support procedure CO-58Wrong place of service CO-146Diagnosis invalid for date of service CO-181Procedure code invalid for date of service CO-182Modifier invalid for date of service CO-189Not otherwise classified code CO-199Revenue code and procedure code mismatch CO-B16New patient qualifications not met

Bundling / modifier

CO-59Multiple or concurrent procedure rules CO-97Included in another service CO-234Procedure not paid separately CO-236Procedure or modifier combination not compatible CO-B15Qualifying service not paid

Missing information

CO-16Claim lacks information CO-107Related claim not paid CO-125Submission or billing error CO-226Information requested not provided CO-227Patient did not provide information CO-252Attachment or documentation required

Medical necessity

CO-50Not medically necessary CO-151Frequency not supported

Duplicate claim

CO-18Duplicate claim

Timely filing

CO-29Timely filing limit passed

Other insurance (COB)

Provider enrollment

CO-170Not paid when billed by this provider type CO-185Rendering provider not eligible CO-242Services not provided by network provider CO-B7Provider not certified for this service

Not covered

CO-49Routine or preventive exam not covered CO-54Multiple surgeons or assistant not covered CO-55Experimental or investigational CO-96Non-covered charge CO-119Benefit maximum reached CO-167Diagnosis not covered CO-204Not covered under the patient's current plan CO-273Coverage or plan year limit

Other

CO-A1Claim or service denied

Common remark codes (RARC)

M15	Separately billed services were bundled because they are part of another procedure.
M20	The HCPCS code is missing or incomplete.
M51	The procedure code is missing, incomplete or invalid.
M76	The diagnosis code is missing, incomplete or invalid.
M77	The place of service is missing, incomplete or invalid.
M80	Not covered when performed during the same session as another approved procedure.
M86	Service denied because payment was already made for a similar procedure in the same time frame.
MA04	The secondary payment cannot be processed without the primary payer's information.
MA07	The claim was forwarded to Medicaid or a supplemental insurer.
MA13	Information is needed from the patient (for example other insurance or accident details).
MA18	The claim was forwarded to the patient's supplemental insurer.
MA63	The principal diagnosis is missing or invalid.
MA120	The CLIA certification number is missing or invalid.
MA130	The claim has incomplete or invalid information. Fix it and submit a new claim (no appeal rights).
N4	The prior insurance carrier's EOB is missing or incomplete.
N20	Service not payable with other service rendered on the same date.
N30	The patient is not eligible for this service.
N54	The claim was reviewed against a medical policy.
N95	This provider type or specialty may not bill this service.
N115	Decision based on a Local Coverage Determination (LCD). Check the LCD for covered diagnoses.
N130	Check the plan benefit documents or the payer's policy for this service.
N179	Additional information was requested from the patient or provider.
N290	The rendering provider's identifier is missing or invalid.
N381	Consult the provider contract for the rules that applied to this payment.
N386	This decision was based on a National Coverage Determination (NCD).
N432	Adjustment based on a recovery audit.
N522	Duplicate of a claim processed or in process on another claim.
N657	This should be billed with the appropriate code for these services.

Plain-English summaries for billing staff. The official code wording is maintained by X12 at x12.org/codes.

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