CO-4Contractual ObligationCoding
CO-4 Denial Code: Procedure code inconsistent with modifier
The procedure code is inconsistent with the modifier used, or a required modifier is missing.
Why CO-4 happens
- ●Missing required modifier (e.g., 25, 59, LT/RT)
- ●Modifier used does not match the procedure code
- ●Bilateral procedure billed without the correct modifier
How to fix a CO-4 denial
- 1
Review the procedure code and payer modifier rules
- 2
Append or correct the modifier per NCCI edits
- 3
Resubmit as a corrected claim
How to prevent it
Run claims through NCCI/modifier scrubbing edits before submission.
Drowning in CO-4 denials?
OakClaim works every denial within 48 hours and builds prevention rules so they stop recurring.