CO 231 denial code
Claim adjustment reason code 231. Often reported as CO 231.
Mutually exclusive procedures
Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated .
What 231 means
Two procedures billed for the same day or setting are considered mutually exclusive, so only one of them is paid.
Mutually exclusive pairs are services that would not reasonably be done together on the same patient at the same session, often because one is an alternative to the other.
The payer usually pays the one with the higher value and denies the other. A policy reference may appear on the remittance explaining which edit applied.
Group codes seen with 231
On a remittance, 231 comes after a group code. These are the ones it is most often reported with:
- CO 231 (Contractual Obligation): The provider's side of the ledger. The reduction comes from the payer contract or a rule the provider has to follow, and the patient normally cannot be billed for it.
The payer chooses the group code for each adjustment, so the same reason code can appear with another group code on your remittance. Read the two together. More about group codes.
Common causes
- Two codes describing alternative approaches to the same procedure were both billed.
- An open and a laparoscopic version of related procedures were billed together.
- Coding picked both an initial and a different-method code for the same service.
What to do next
- Check which procedure was actually done and whether both were truly separate.
- Remove the extra code and accept the payment when the edit is correct.
- Appeal with the procedure note if the services were done at separate sites or sessions.
- Use a distinct service modifier only when the documentation supports it.
Related codes
- 236 (reason code) Procedure combo conflicts same day
- 234 (reason code) Procedure not paid separately
- 97 (reason code) Service included in another payment
- 4 (reason code) Procedure code and modifier do not match
Source
Official wording: X12 Claim Adjustment Reason Codes list. The explanation on this page is our own plain-English wording, not the X12 text.
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