CARC 4: Modifier missing or inconsistent with the procedure code

Group code context

Usually sent with group code CO (contractual obligation): under your contract you cannot bill the patient for this amount.

Common causes

• Missing modifier 25 on an E/M billed with a procedure the same day
• Missing laterality modifier such as RT or LT
• Modifier 59 or X-modifier used where it does not apply
• Professional or technical component modifier (26 or TC) missing

Step-by-step fix

1. Read the claim line and the code's modifier rules
2. Check the documentation supports the modifier
3. Add or correct the modifier
4. Send a corrected claim (frequency code 7 for most payers), not a new claim

Appeal guidance

If the modifier was correct and supported, appeal with the notes that support it.

When not to appeal

Do not appeal if the documentation does not support the modifier. Fix the claim or accept the denial.

Prevention checklist

• Build modifier edits into your claim scrubber
• Train providers on modifier 25 documentation
• Review NCCI edits for common code pairs

Related codes

CARC 16: Claim lacks information or has billing errors

CARC 97: Included in another service (bundled)

Source and review

Last checked: 2026-10-05