Remittance advice
Denial codes explained
Claim adjustment reason codes (CARCs) appear on every remittance advice, prefixed by a group code that says who absorbs the amount: CO (contractual obligation, provider write-off), PR (patient responsibility, billable to the patient), OA (other adjustment), or PI (payer-initiated reduction). Each page below explains one code in plain English: what it means, why it happens, and how to fix and prevent it.
CO - contractual obligation (provider write-off)
| Code | What it means |
|---|---|
| CO A1 | What denial code CO A1 means, why the real reason lives in the remark codes, and how to work these denials without guessing. |
| CO 4 | Denial code CO 4 means the procedure code and modifier don't line up, or a required modifier is missing. How to correct the claim and resubmit. |
| CO B7 | What denial code CO B7 means, how enrollment lapses and CLIA certificate problems trigger it, and how to get affected claims reprocessed. |
| CO 11 | Denial code CO 11 means the diagnosis on the claim doesn't support the procedure billed. How to check the LCD, fix the coding, and resubmit. |
| CO B15 | What denial code CO B15 means, why add-on codes deny without their primary procedure, and how to fix the claim pairing. |
| CO 16 | Denial code CO 16 means the claim lacks information or has a billing error. The paired remark code says what's missing. How to find it and resubmit. |
| CO 18 | Denial code CO 18 means the payer already has this claim. How to check the status of the original before resubmitting, and when a modifier is the fix. |
| CO 22 | Denial code CO 22 means coordination of benefits points to a different primary payer. How to sort out payer order, fix COB, and rebill correctly. |
| CO 24 | Denial code CO 24 usually means a Medicare Advantage patient was billed to traditional Medicare. How to find the right plan and rebill the claim. |
| CO 29 | Denial code CO 29 means the claim arrived after the filing deadline, 12 months for Medicare. When an exception applies and when to write it off. |
| CO 45 | What denial code CO 45 means on a remittance advice, why it appears, and when to write it off, appeal it, or fix the claim. |
| CO 50 | Denial code CO 50 means the payer decided the service wasn't medically necessary. Why appeals beat resubmission, and how ABNs shift liability. |
| CO 59 | Denial code CO 59 flags a payment cut under multiple procedure rules (MPPR), not a denial. How to verify the ranking and when to dispute it. |
| CO 96 | Denial code CO 96 means the payer doesn't cover the charge. Read the remark code, then decide: fix a billing error, appeal, or write it off. |
| CO 97 | Denial code CO 97 means the payment for this service is included in another service already adjudicated: NCCI edits or the global period. What to do next. |
| CO 109 | What denial code CO 109 means, how to find the correct payer or Medicare contractor, and when to resubmit instead of appeal. |
| CO 119 | What denial code CO 119 means, why claims deny when a benefit limit is exhausted, and when to appeal, bill secondary coverage, or write off. |
| CO 151 | Denial code CO 151 means the billed units or frequency exceed what the payer's information supports (MUE or frequency limits). How to respond. |
| CO 167 | What denial code CO 167 means, why the billed diagnosis fails payer coverage policy, and how to correct the claim or appeal with documentation. |
| CO 170 | What denial code CO 170 means, why payment is denied for this provider type or specialty, and how to fix enrollment or billing setup. |
| CO 197 | What denial code CO 197 means, why claims deny for missing precertification, and how to pursue retro authorization or appeal. |
| CO 198 | What denial code CO 198 means, why claims deny when services go beyond the authorized units or visits, and how to expand the auth or appeal. |
| CO 204 | What denial code CO 204 means, why a service, drug, or equipment falls outside the patient's benefit plan, and what to do next. |
| CO 226 | What denial code CO 226 means, why claims deny when a payer's information request goes unanswered, and how to respond and get the claim reprocessed. |
| CO 231 | What denial code CO 231 means, how NCCI mutually exclusive edits work, and when a modifier, corrected claim, or write-off is the right response. |
| CO 234 | What denial code CO 234 means, how to read the paired remark code, and when to add a modifier, correct the claim, or write off the line. |
| CO 236 | What denial code CO 236 means, how NCCI and fee schedule rules flag same-day code conflicts, and how to correct, appeal, or write off. |
| CO 242 | What denial code CO 242 means, why claims deny when care comes from outside the plan's network or designated providers, and how to respond. |
| CO 252 | What denial code CO 252 means, how to find which attachment the payer wants, and how to submit records so the claim can be adjudicated. |
| CO 253 | What code CO 253 means, how the 2% Medicare sequestration reduction is calculated, and how to post it as a contractual adjustment. |
| CO 256 | What denial code CO 256 means, why managed care contracts exclude services from payment, and when an appeal is worth filing. |
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OA - other adjustment
| Code | What it means |
|---|---|
| OA 23 | What code OA 23 means on a secondary remittance, how to reconcile it against the primary payer's adjudication, and how to post it. |
PR - patient responsibility
| Code | What it means |
|---|---|
| PR 1 | What code PR 1 means, how deductible amounts flow to patient responsibility, and how to post and collect them correctly. |
| PR 2 | What code PR 2 means, how coinsurance is calculated from the allowed amount, and how to post and collect it without balance-billing errors. |
| PR 3 | What code PR 3 means, how copays differ from coinsurance and deductibles, and how to post and collect them cleanly. |
| PR 26 | What denial code PR 26 means, how to confirm the patient's coverage start date, and when the balance can go to the patient. |
| PR 27 | What denial code PR 27 means, how to confirm the patient's coverage end date, and when you can bill the patient. |
| PR 31 | What denial code PR 31 means, how to fix identity and member ID mismatches, and when the balance genuinely belongs to the patient. |
| PR 49 | What denial code PR 49 means, why routine exams and screenings deny, and how to tell a coding error from a true non-covered service. |
| PR 96 | What denial code PR 96 means, how a valid ABN determines Medicare patient billing, and how it differs from CO 96. |
| PR 204 | What denial code PR 204 means, how it differs from CO 204, and how to confirm the exclusion before billing the patient. |
| PR 227 | What denial code PR 227 means, why payer requests to patients go unanswered, and how to get the claim paid once the information arrives. |
Denials tied to fee schedule amounts often pair with questions about what a code should have paid; check the Medicare RVU calculator. Setting-related denials usually involve place of service codes.