Mutually exclusive procedures
Two procedures on the claim cannot reasonably be done together on the same day under the payer's coding edits (NCCI mutually exclusive edits).
CO = Contractual Obligation. The provider owes the difference. The patient cannot be billed for this amount. The same reason code can appear with a different group code; the group decides who may be billed.
Usual causes
- Two codes that describe the same work in different ways.
- Separate anatomic sites or sessions not shown with a modifier.
- Coding a comprehensive code and a component code together.
The fix
Check the NCCI edit for the pair and the modifier indicator. If a modifier is allowed and the documentation supports separate sites or sessions, add it and send a corrected claim. If not, bill only the correct code.
Appeal or corrected claim?
Corrected claim with a modifier when supported; otherwise a write-off.
Deadline to watch
Timely filing limit.
Exact limits are in your payer contract or provider manual. When in doubt, send the correction or appeal this week.
CO-231 in short
What does CO-231 mean?
Two procedures on the claim cannot reasonably be done together on the same day under the payer's coding edits (NCCI mutually exclusive edits). The official X12 text reads: "Mutually exclusive procedures cannot be done in the same day/setting. Usage: Refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment Information REF), if present."
What usually causes a CO-231 denial?
Two codes that describe the same work in different ways. Separate anatomic sites or sessions not shown with a modifier. Coding a comprehensive code and a component code together.
How do I fix CO-231?
Check the NCCI edit for the pair and the modifier indicator. If a modifier is allowed and the documentation supports separate sites or sessions, add it and send a corrected claim. If not, bill only the correct code.
Should I appeal CO-231 or send a corrected claim?
Correct or appeal (see note). Corrected claim with a modifier when supported; otherwise a write-off.
What deadline applies to CO-231?
Timely filing limit.