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CO-221 Denial Code (Deactivated): Claim Under Investigation

CO-221 meant a property and casualty payer was holding the claim because it was under investigation. X12 deactivated it and its notes point payers to code P8.

X12 deactivated CARC221 on July 1, 2014. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals.

Code: CO-221 (CARC 221)
Status: Deactivated StoppedJuly 1, 2014 (in use since January 27, 2008).
Code set: Claim Adjustment Reason Codes (CARC)
Group codes: CO (Contractual Obligation): Payment was withheld pending the investigation; it did not shift liability to the patient.
Official description: Claim is under investigation. Note: If adjustment is at the Claim Level, the payer must send and the provider should refer to the 835 Insurance Policy Number Segment (Loop 2100 Other Claim Related Information REF qualifier 'IG') for the jurisdictional regulation. If adjustment is at the Line Level, the payer must send and the provider should refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment information REF). (Note: To be used by Property & Casualty only)
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What CO-221 meant

CARC 221 was used by property and casualty payers, including auto and workers’ compensation carriers, to say they would not decide the claim yet because it was under investigation. It was effectively a hold, with the code text pointing to where the relevant jurisdictional regulation should be reported on the 835.

What replaced it

X12’s note says to use P8. CO-P8 keeps the same meaning in the property and casualty P-series. When the delay is due to litigation rather than an investigation, payers use OA-P11. Outside property and casualty, a line pending further review may carry OA-133.

If you still see CO-221

It will appear in older files, but the situation is the same today. Find out who the adjuster is and what the investigation concerns, and send any records or statements they need. Set follow-up reminders, since investigations can take time. Ask whether state rules require the payer to decide within a certain period, and whether you may bill other coverage while you wait.

CO-P8 (Claim is under investigation.): Named replacement: claim is under investigation.
OA-P11 (The disposition of the related Property & Casualty claim (injury or illness) is pending due to litigation.): The related property and casualty claim is pending due to litigation.
OA-133 (The disposition of this service line is pending further review. (Use only with Group Code OA).): The disposition of the service line is pending further review, used with group OA.

CO-221 FAQ

What kinds of investigations lead to this code?

Payers may investigate how an injury happened, whether coverage applies, or whether there are signs of fraud. The code does not say which; the adjuster can tell you the status.

Should I resubmit while a claim is under investigation?

Usually no. Resubmitting can create duplicates. Keep in contact with the adjuster and supply any information they request.

Important: read before using this information

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