> ## Documentation Index
> Fetch the complete documentation index at: https://mso.getlemma.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Denial code playbook

> Action-oriented table of the top denial scenarios: root cause, fix-or-appeal decision, and the prevention change that stops it recurring.

The operational companion to [CARC codes](/reference/edi/carc-codes). For each scenario: what actually happened, whether to correct or appeal, and what to change upstream so it stops.

**How to use it:** work your queue by CARC family, look up the scenario, take the action, and implement the prevention. The prevention column is the one that compounds.

**This is not the full code set.** CARC and RARC codes and their definitions are copyrighted and licensed by X12; reproducing the complete lists requires a license from X12, so this page (and [CARC codes](/reference/edi/carc-codes) and [RARC codes](/reference/edi/rarc-codes)) cover only the highest-volume scenarios a biller actually needs, not an exhaustive reference. For a code that isn't here, look it up at the authoritative source, [x12.org/codes](https://x12.org/codes/claim-adjustment-reason-codes), and apply the same fix-or-appeal logic as the nearest scenario in this table.

## Eligibility

| CARC / RARC                                  | Root cause                                              | Fix or appeal                                                  | Prevention                                      |
| -------------------------------------------- | ------------------------------------------------------- | -------------------------------------------------------------- | ----------------------------------------------- |
| **CO-26**, expenses prior to coverage        | Service before the effective date                       | Verify; rebill correct payer, or bill the patient if permitted | Run eligibility at scheduling **and** check-in  |
| **CO-27**, coverage terminated               | Coverage lapsed before service                          | Verify; find current coverage; rebill                          | Re-check at check-in, not just at booking       |
| **CO-31**, patient not identified as insured | Wrong member ID, name mismatch, or missing alpha prefix | **Correct and resubmit**                                       | Scan the card; verify against the 271           |
| **CO-32**, not an eligible dependent         | Relationship or dependent coverage issue                | Verify; rebill or bill the patient                             | Capture relationship accurately at registration |
| **CO-177**, eligibility requirements not met | Plan-specific requirement                               | Verify with the payer                                          | Read the 271 fully, not just "active"           |

## Authorization

| CARC / RARC                                          | Root cause                                           | Fix or appeal                                            | Prevention                                                                                   |
| ---------------------------------------------------- | ---------------------------------------------------- | -------------------------------------------------------- | -------------------------------------------------------------------------------------------- |
| **CO-197**, authorization absent, **auth exists**    | Obtained but never entered in the structured field   | **Corrected claim** (freq. 7) with the auth number       | **Scrubber edit** blocking submission when a CPT on the payer's auth list has no auth number |
| **CO-197**, no auth obtained                         | Auth requirement missed at scheduling                | Request retro-auth; else **appeal** on medical necessity | Per-payer auth-required list built into scheduling                                           |
| **CO-198**, authorization exceeded                   | Units or visits beyond what was authorized           | Request additional units; appeal                         | Track authorized units against delivered units                                               |
| **CO-15**, auth invalid or doesn't apply             | Auth doesn't match CPT, dates, provider, or facility | Verify and correct, or obtain a matching auth            | Verify auth details against the planned service before the visit                             |
| **N54**, claim inconsistent with authorized services | Same                                                 | Same                                                     | Same                                                                                         |

## Coding and medical necessity

| CARC / RARC                                                | Root cause                                             | Fix or appeal                                                                  | Prevention                                         |
| ---------------------------------------------------------- | ------------------------------------------------------ | ------------------------------------------------------------------------------ | -------------------------------------------------- |
| **CO-11**, diagnosis inconsistent with procedure           | Code pairing doesn't support the service               | Review; **correct** if wrong, **appeal** with documentation if right           | Scrubber code-pair edits; clinician education      |
| **CO-4**, modifier missing or inconsistent                 | Required modifier absent                               | **Correct and resubmit**                                                       | Scrubber modifier edits by code                    |
| **CO-50**, not medically necessary                         | Coverage policy not met, or documentation insufficient | **Appeal** citing the payer's own policy and the LCD/NCD                       | Know your MAC's LCDs; document to the criteria     |
| **CO-97**, bundled                                         | NCCI edit; included in another service's allowance     | Verify the edit. Modifier 59 or an X-modifier **only if clinically justified** | Run NCCI edits pre-submission                      |
| **CO-151**, information doesn't support this many services | Units or frequency                                     | Appeal with documentation                                                      | Document units and time explicitly                 |
| **CO-167**, diagnosis not covered                          | Benefit or coverage policy                             | Verify; usually not appealable                                                 | Check coverage before scheduling elective services |
| **M81**, code to highest specificity                       | Unspecified ICD-10 code used                           | **Correct** to a specific code                                                 | Scrubber edit flagging unspecified codes           |

**Modifier 59 and the X-modifiers are enforcement-visible.** Using them to bypass an NCCI edit without a genuine clinical basis is a recognized unbundling pattern. Use them where the clinical circumstances justify them and document why. See [Billing compliance basics](/concepts/compliance/billing-compliance-basics).

## Timely filing

| CARC                                                      | Root cause                                       | Fix or appeal                                                                                                 | Prevention                                                          |
| --------------------------------------------------------- | ------------------------------------------------ | ------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------- |
| **CO-29**, filing limit expired, **was submitted timely** | Payer lost it, or it bounced in a rejection loop | **Appeal** with the clearinghouse acceptance report                                                           | Weekly **no-acceptance report**; same-day rejection work            |
| **CO-29**, genuinely late                                 | Charge entry lag, or a held claim aged out       | Check exceptions: retro eligibility, COB delay, retro-effective enrollment. Else write off with a root cause. | Same-day charge entry; internal deadline inside the contractual one |

## Coordination of benefits

| CARC                                           | Root cause                                           | Fix or appeal                              | Prevention                                          |
| ---------------------------------------------- | ---------------------------------------------------- | ------------------------------------------ | --------------------------------------------------- |
| **CO-22**, may be covered by another payer     | Wrong payer billed first                             | Determine order; bill the primary          | Ask about other coverage at every registration      |
| **OA-23**, prior payer adjudication            | Informational on secondary claims                    | Not a denial                               | —                                                   |
| **N4**, missing prior carrier EOB              | Secondary claim submitted without primary remittance | **Resubmit** with the primary's 835 detail | Automate primary-EOB attachment on secondary claims |
| **MA04**, secondary needs primary payment info | Same                                                 | Same                                       | Same                                                |

## Credentialing and enrollment

| CARC                                                     | Root cause                                            | Fix or appeal                                | Prevention                                                 |
| -------------------------------------------------------- | ----------------------------------------------------- | -------------------------------------------- | ---------------------------------------------------------- |
| **CO-8**, procedure inconsistent with provider type      | **Taxonomy mismatch** with enrollment                 | Correct the taxonomy; verify enrollment      | Verify claim taxonomy matches enrolled taxonomy at go-live |
| **CO-185**, rendering provider not eligible              | Not credentialed, or not linked to the group contract | Resolve with payer enrollment, then rebill   | Don't schedule insured patients before the effective date  |
| **CO-206**, NPI missing or invalid                       | EDI enrollment incomplete, or wrong NPI on the claim  | Verify EDI enrollment and claim data         | Test one claim per payer before volume                     |
| **CO-B7**, not certified for this procedure on this date | **Service date before the provider's effective date** | Pursue retro-effective date; else unbillable | Track effective dates in the credentialing grid            |
| **CO-109**, not covered by this payer/contractor         | Wrong payer or MAC                                    | Rebill correctly                             | Verify payer ID mapping                                    |

## Duplicates

| CARC                          | Root cause                                             | Fix                                                            | Prevention                                                       |
| ----------------------------- | ------------------------------------------------------ | -------------------------------------------------------------- | ---------------------------------------------------------------- |
| **CO-18**, exact duplicate    | You resubmitted an adjudicated claim as a new original | Use **frequency code 7** referencing the original claim number | Train billers: adjudicated claims get corrected, not resubmitted |
| **N522**, duplicate crossover | Medicare crossover already sent it to the secondary    | Don't submit the secondary separately when crossover applies   | Know which payers auto-crossover                                 |

## Non-covered, usually not errors

| CARC                                   | Meaning                        | Action                                                  |
| -------------------------------------- | ------------------------------ | ------------------------------------------------------- |
| **CO/PR-96**, non-covered charge       | Read the RARC. Benefit design. | Patient responsibility with proper notice, or write off |
| **PR-204**, not covered under the plan | Benefit design                 | Patient responsibility                                  |
| **CO-253**, sequestration              | Statutory Medicare reduction   | Write off                                               |

<Tip>
  **Train billers to recognize the non-errors.** CO-45, PR-1/2/3, CO-253, CO-97, and CO-96 generate large volumes of wasted appeal effort in practices that treat every adjustment as a denial.
</Tip>

## Information requests

| CARC / RARC                                         | Action                                                    |
| --------------------------------------------------- | --------------------------------------------------------- |
| **CO-252**, attachment required                     | Submit the documentation via the payer's required channel |
| **CO-16 + a RARC**                                  | **Read the RARC**, it names the missing element           |
| **CO-226**, provider information not provided       | Respond; the clock may be running                         |
| **MA130**, incomplete/invalid, **no appeal rights** | **Submit a new claim.** Do not appeal.                    |

## The prevention priority list

If you fix things in order of value, this is the order:

1. **Eligibility at scheduling and check-in**, with the 271 saved
2. **A scrubber edit blocking submission when an authorization is required and missing**
3. **Same-day rejection work**, plus a weekly no-acceptance report
4. **Taxonomy and enrollment data verified** at every payer go-live
5. **Effective-date discipline**, no insured patients before a clinician's effective date
6. **Same-day charge entry**
7. **NCCI and modifier edits** in the scrubber
8. **Automated primary-EOB attachment** on secondary claims

Items 1–5 prevent the majority of denials in most practices, and four of them are enrollment or front-desk controls rather than billing ones.


## Related topics

- [Your first denial](/start/first-90-days/work-your-first-denial.md)
- [Claim denials, explained](/concepts/payments/claim-denials.md)
- [Work the denial queue](/guides/billing/work-the-denial-queue.md)
- [File appeals](/guides/billing/file-appeals.md)
- [Submit clean claims](/guides/billing/submit-clean-claims.md)
- [CARC codes (Claim Adjustment Reason Codes)](/reference/edi/carc-codes.md)
- [RARC codes (Remittance Advice Remark Codes)](/reference/edi/rarc-codes.md)
- [Group codes (CO, PR, OA, PI)](/reference/edi/group-codes.md)