CO-231: Mutually Exclusive Procedures
Two procedures are mutually exclusive. Check if a modifier override is permitted by NCCI and resubmit if applicable.
What Does CO-231 Mean?
With CO, the mutually exclusive denial is a coding/contractual matter. Review NCCI edits and apply appropriate modifiers if a legitimate override exists.
CARC 231 indicates that two or more procedures billed on the same claim are classified as mutually exclusive per the National Correct Coding Initiative (NCCI) or the payer's own coding edits. Mutually exclusive procedures are those that, by definition, cannot reasonably be performed at the same session on the same patient — such as two different approaches to the same anatomical site or two procedures that represent alternative methods for the same clinical objective.
The payer will typically pay the higher-valued procedure and deny the mutually exclusive one. This differs from bundling (where one procedure is a component of another) — mutually exclusive means the two procedures represent contradictory approaches.
Common Causes
| Cause | Frequency |
|---|---|
| Two mutually exclusive procedures billed on the same date The claim includes two procedure codes that are considered mutually exclusive per NCCI or payer edits and cannot both be performed on the same patient on the same date of service | Most Common |
| NCCI mutually exclusive edit triggered The National Correct Coding Initiative (NCCI) identifies the procedure combination as mutually exclusive, meaning the two procedures cannot logically be performed together | Most Common |
| Procedures represent different approaches to the same treatment The two procedures billed represent alternative methods of performing the same service (e.g., open vs. laparoscopic approach) and only one can be reimbursed | Common |
| Modifier not used or not accepted for mutually exclusive override A modifier that might override the mutually exclusive edit was not used or the edit does not allow modifier overrides | Common |
How to Resolve
- Check NCCI edit tables Verify the mutually exclusive relationship and modifier override status.
- Apply modifiers if allowed Add modifier 59 or XE/XS/XP/XU if the procedures were genuinely separate.
- Resubmit with documentation Resubmit with modifiers and supporting clinical documentation.
Appeal if both procedures were clinically necessary and genuinely performed as separate and distinct services. Include detailed operative notes, clinical documentation supporting the medical necessity of both procedures, and appropriate modifiers (59, XE, XS, XP, XU). Reference NCCI guidelines that permit modifier override for the specific edit.
Common RARC Pairings
The RARC code tells you exactly what triggered the CO-231:
| RARC | Description |
|---|---|
| N522 | Adjustment based on a review of the coding. Review the coding combination and correct per NCCI mutually exclusive edit requirements → |
| M15 | Separately billed services/tests have been bundled as they are considered components of the same procedure. Verify whether the procedures are truly mutually exclusive or can be unbundled with appropriate documentation → |
How to Prevent CO-231
- Implement claim scrubbing with NCCI edit checks before submission
- Train coding staff on mutually exclusive procedure pairs and appropriate modifier use
- Use modifier 59 and its sub-modifiers correctly to distinguish separate services
General Prevention
- Implement NCCI edit checking in your claim scrubbing software before submission
- Train coders on mutually exclusive procedure pairs and when modifiers can and cannot be used
- Review NCCI PTP edit tables regularly for updates to mutually exclusive procedure pairs
- Ensure clinical documentation supports separate and distinct procedures when modifiers are used
- Conduct regular coding audits focusing on mutually exclusive procedure pairs
Also Filed As
The same CARC 231 may appear with different Group Codes:
Related Denial Codes
Sources
- https://x12.org/codes/claim-adjustment-reason-codes
- https://portal.ct.gov/-/media/ohs/health-it-advisory-council/apcd-advisory-group/data-submission-guide-workgroup/meeting-materials/6-30-22/carc-codes_final.pdf
- https://www.aapc.com/resources/claim-adjustment-reason-codes
- Codes maintained by X12. Visit x12.org for official definitions.