CO-4 denial code
The modifier on the line doesn't fit the procedure code, or a modifier the payer requires is missing.
“The procedure code is inconsistent with the modifier used. …”
Start 01/01/1995 · Last modified 03/01/2020 · X12 adjustment reason code list
What it usually means in behavioral health
Behavioral health claims carry more modifiers than most. Telehealth (95, 93, or FQ depending on payer and modality), provider-level modifiers some Medicaid programs require (such as HO, HN, or HP for degree level), and payer-specific ABA and program modifiers are the usual suspects.
When the problem is a missing modifier, the remark code is often N822.
Common causes
- Telehealth modifier missing, or the wrong one for the payer or for audio-only service
- Provider-level modifier missing or inconsistent with the rendering clinician's credential
- A modifier used with a code it isn't valid for
- A payer-specific program or ABA modifier left off
Correct and resubmit, or appeal?
Correct and resubmit with the modifier the payer's billing rules require for that code, setting, and clinician. Appeal only if the payer applied a modifier rule its own manual doesn't contain.
What to do
Look up the payer's modifier rules for the exact code and place of service.
Check the rendering clinician's credential against any provider-level modifier.
Fix the modifier logic in your billing system, then resubmit.
Often seen with
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