What is a CARC denial code?

A Claim Adjustment Reason Code (CARC) is the code on a remittance advice that explains why a payer adjusted or denied a line. It is paired with a group code - CO, PR, OA, or PI - that determines who absorbs the balance. CARCs are often accompanied by RARC remark codes that add specifics.

What is the difference between CO and PR denial codes?

CO means contractual obligation: the provider absorbs the balance and cannot bill the patient. PR means patient responsibility: the balance transfers to the patient. Mistaking a CO code for a PR code and billing the patient is a contract violation.

Which denial codes are the most common?

CO-16 (missing or invalid information) is the highest-volume denial in most practices, followed by CO-197 (missing prior authorization), CO-97 (bundled service), CO-18 (duplicate claim), and CO-29 (timely filing expired). CO-29 is typically the most costly because it is rarely overturned.

Can every denial be appealed?

No. Some denials are correct adjustments rather than errors - CO-45 records a normal contractual write-off, and PR-1 through PR-3 record ordinary patient cost sharing. Others, such as a bundling edit with modifier indicator 0, cannot be bypassed regardless of documentation. Identifying which denials are genuinely appealable is what makes A/R work efficient.

CARC Denial Code Reference

All 59 CARC denial codes in one table - the group code, what each one means in plain English, and who absorbs the balance. Every code links to a full page covering why it happens, the steps to work it, and whether it is worth appealing.

Denial codes tell you what went wrong; the payer's own policy tells you how to fix it. For deadline-driven codes like CO-29 and authorization denials like CO-197, check the payer billing reference for that payer's verified filing limits and appeal windows.

Group codes: who the balance belongs to

CO - Provider: Contractual Obligation - the provider absorbs the balance and cannot bill the patient
PR - Patient: Patient Responsibility - the balance transfers to the patient
OA - Neither - adjustment: Other Adjustment - typically a coordination-of-benefits or crossover adjustment
PI - Provider: Payer Initiated Reduction - the payer's own determination, not a contract term

All 59 CARC codes

Showing 59 of 59 codes

CARC denial codes with their group code, plain-English meaning, and who absorbs the balance. Each code links to a full reference page.
Code	Group	What it means	Who pays
CO-4Provider	CO	The modifier does not match the procedure code billed	Provider
CO-5Provider	CO	The procedure does not match the place of service billed	Provider
CO-6Provider	CO	The procedure does not match the patient's age	Provider
CO-8Provider	CO	The procedure does not match the provider's type or specialty	Provider
CO-11Provider	CO	The diagnosis does not support the procedure billed	Provider
CO-16Provider	CO	Claim or service lacks required information	Provider
CO-18Provider	CO	Exact duplicate claim or service	Provider
CO-19Workers' comp carrier	CO	The claim belongs to a work-related injury carrier	Workers' comp carrier
CO-22Another payer	CO	Care may be covered by another payer per coordination of benefits	Another payer
CO-24Another payer	CO	Charges are covered under a capitation or managed care arrangement	Another payer
CO-27Patient or new plan	CO	Expenses were incurred after coverage terminated	Patient or new plan
CO-29Provider	CO	The time limit for filing has expired	Provider
CO-31Provider	CO	The patient cannot be identified as an insured member	Provider
CO-39Provider	CO	Authorization was requested and refused	Provider
CO-45Provider	CO	Charge exceeds the contracted fee schedule amount	Provider
CO-50Provider	CO	Not deemed medically necessary by the payer	Provider
CO-55Provider	CO	The service is considered experimental or investigational	Provider
CO-58Provider	CO	The payer considers the treatment setting inappropriate	Provider
CO-59Provider	CO	Payment reduced under multiple or concurrent procedure rules	Provider
CO-96Provider	CO	Non-covered charge the provider absorbs	Provider
CO-97Provider	CO	Service is bundled into another service already adjudicated	Provider
CO-107Provider	CO	The related or qualifying service was not identified on the claim	Provider
CO-109Another payer	CO	Claim not covered by this payer or contractor	Another payer
CO-119Provider	CO	The benefit maximum for this period has been reached	Provider
CO-140Provider	CO	The patient's identification number and name do not match	Provider
CO-146Provider	CO	The diagnosis was invalid for the date of service	Provider
CO-147Provider	CO	The contracted rate has expired or is not on file	Provider
CO-151Provider	CO	Payer deems the information does not support this many services	Provider
CO-167Provider	CO	The diagnosis is not covered by this plan	Provider
CO-170Provider	CO	This provider type may not be paid for this service	Provider
CO-181Provider	CO	The procedure code was not valid on the date of service	Provider
CO-183Provider	CO	The referring provider is not eligible to refer this service	Provider
CO-185Provider	CO	The rendering provider is not eligible to perform this service	Provider
CO-197Provider	CO	Precertification, authorization, or notification is absent	Provider
CO-198Provider	CO	The authorized limit for this service was exceeded	Provider
CO-226Provider	CO	Requested information was not received from the provider	Provider
CO-231Provider	CO	Mutually exclusive procedures were billed for the same encounter	Provider
CO-234Provider	CO	This procedure is not paid separately	Provider
CO-236Provider	CO	Procedure combination is not compatible with another procedure	Provider
CO-243Provider	CO	Services were not authorized by the network or primary care provider	Provider
CO-252Provider	CO	An attachment or additional documentation is required	Provider
CO-256Another payer	CO	The service is not payable under the managed care contract	Another payer
PR-1Patient	PR	Amount applied to the patient's deductible	Patient
PR-2Patient	PR	Amount applied to the patient's coinsurance	Patient
PR-3Patient	PR	Amount applied to the patient's copayment	Patient
PR-26Patient, if no other plan	PR	Expenses were incurred before coverage began	Patient, if no other plan
PR-33Patient, if no other plan	PR	The policy has no dependent coverage	Patient, if no other plan
PR-35Patient	PR	The lifetime benefit maximum has been reached	Patient
PR-49Patient, with notice	PR	A routine or screening exam the plan does not cover	Patient, with notice
PR-51Disputed - challenge it	PR	A pre-existing condition exclusion was applied	Disputed - challenge it
PR-96Patient, with notice	PR	Non-covered charges	Patient, with notice
PR-200Patient, unless reinstated	PR	Expenses were incurred during a lapse in coverage	Patient, unless reinstated
PR-204Patient, with notice	PR	Service not covered under the patient's current benefit plan	Patient, with notice
PR-242Patient, if not protected	PR	Services were not provided by network providers	Patient, if not protected
OA-23Neither - adjustment	OA	Impact of prior payer's adjudication	Neither - adjustment
OA-100Patient (already paid)	OA	Payment was made to the patient instead of the provider	Patient (already paid)
OA-121Neither - adjustment	OA	An indemnification adjustment was applied	Neither - adjustment
PI-222Provider	PI	The contracted maximum units for this period were exceeded	Provider
PI-223Provider	PI	An adjustment required by federal, state, or local law	Provider

Denial code frequently asked questions

What is a CARC denial code?: A Claim Adjustment Reason Code (CARC) is the code on a remittance advice that explains why a payer adjusted or denied a line. It is paired with a group code - CO, PR, OA, or PI - that determines who absorbs the balance. CARCs are often accompanied by RARC remark codes that add specifics.
What is the difference between CO and PR denial codes?: CO means contractual obligation: the provider absorbs the balance and cannot bill the patient. PR means patient responsibility: the balance transfers to the patient. Mistaking a CO code for a PR code and billing the patient is a contract violation.
Which denial codes are the most common?: CO-16 (missing or invalid information) is the highest-volume denial in most practices, followed by CO-197 (missing prior authorization), CO-97 (bundled service), CO-18 (duplicate claim), and CO-29 (timely filing expired). CO-29 is typically the most costly because it is rarely overturned.
Can every denial be appealed?: No. Some denials are correct adjustments rather than errors - CO-45 records a normal contractual write-off, and PR-1 through PR-3 record ordinary patient cost sharing. Others, such as a bundling edit with modifier indicator 0, cannot be bypassed regardless of documentation. Identifying which denials are genuinely appealable is what makes A/R work efficient.

These are original plain-English summaries written for reference, not the official X12 code descriptions. Payer handling of any code varies by contract - always verify against the remittance advice and your payer agreement.