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CO-138 Denial Code (Deactivated): Appeal Rules Not Met

CO-138 meant an appeal was not processed because the payer's appeal procedures were not followed or its time limits were missed. X12 deactivated it without naming a successor; CARC 285 and CARC 286 now cover the two situations separately.

X12 deactivated CARC138 on May 1, 2018. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals.

Code: CO-138 (CARC 138)
Status: Deactivated StoppedMay 1, 2018 (in use since June 30, 1999).
Code set: Claim Adjustment Reason Codes (CARC)
Group codes: CO (Contractual Obligation): The provider bore the loss because following the appeal process was its responsibility.
Official description: Appeal procedures not followed or time limits not met.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What CO-138 meant

CARC 138 was a denial of an appeal rather than of the original claim. The payer refused to review the appeal on its merits because the provider either did not follow the required steps, such as using the right form, level, or address, or submitted it after the deadline.

The two problems call for different responses, and the combined code did not say which one applied.

What replaced it

X12 did not name a successor, but two active codes match the halves of the old description:

CO-285 for appeal procedures not followed.
CO-286 for appeal time limits not met.

Do not confuse these with CO-29, which concerns the deadline for filing the original claim.

If you still see CO-138

It may still appear on older appeal outcomes in your A/R. Review the payer’s appeal policy and your submission records. If you can show the appeal arrived on time, send the proof with a request to reopen. If the appeal was simply filed incorrectly and time remains, correct it and resubmit.

When the window has closed, the balance is usually written off. Tracking appeal deadlines by payer in your workflow is the most reliable way to prevent this.

CO-285 (Appeal procedures not followed): Appeal procedures not followed.
CO-286 (Appeal time limits not met): Appeal time limits not met.
CO-29 (The time limit for filing has expired.): The time limit for filing the original claim has expired.

CO-138 FAQ

Can an appeal denied under CO-138 be refiled?

If the problem was procedural, such as a missing form or wrong address, and the deadline has not passed, you can usually resubmit the appeal correctly. If the deadline passed, the payer rarely reopens it without proof of timely filing.

What counts as proof of a timely appeal?

Payer portal confirmations, fax transmission reports, certified mail receipts, or clearinghouse acknowledgments that show the date the appeal was received.

Important: read before using this information

This page is general educational information about a standard industry code set. It is not medical billing, coding, legal, reimbursement, or compliance advice, and it does not create a professional or advisory relationship with ClaimsRevenue.

Code definitions, payer usage, contracts, and laws change, and payers may apply the same code differently. The information is provided “as is,” without warranties of any kind, express or implied, including accuracy, completeness, or currency. You are solely responsible for verifying it against the current official X12 code lists, CMS guidance, your payer contracts, and payer policies before relying on it, and for every billing, coding, collection, and appeal decision you make.

Using this information does not guarantee that any claim will be paid or that any appeal will succeed. To the fullest extent permitted by law, ClaimsRevenue and MOODRX LLC are not liable for any loss or damage arising from its use. Official code descriptions are published by X12 and are quoted for reference only. See our full Claims Validation Disclaimer.