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CO-64 Denial Code (Deactivated): Reversed per Medical Review

CO-64 meant an earlier denial had been overturned following the payer's medical review. It was good news rather than a denial. X12 deactivated it without naming a replacement.

X12 deactivated CARC64 on October 16, 2003. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals.

Code: CO-64 (CARC 64)
Status: Deactivated StoppedOctober 16, 2003 (in use since January 1, 1995).
Code set: Claim Adjustment Reason Codes (CARC)
Group codes: CO (Contractual Obligation): Reported with the corrected payment; nothing was shifted to the patient because of this code.
Official description: Denial reversed per Medical Review.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What CO-64 meant

CARC 64 appeared when a claim that had been denied was looked at again by the payer’s medical review staff and the denial was reversed. It usually accompanied the reprocessed payment and explained why money was now arriving on a claim that had previously been rejected.

What replaced it

X12 did not name a replacement, and none is strictly needed: a reprocessed claim simply comes back with its new payment. The nearest active codes relate to review outcomes rather than reversals:

CO-216 for adjustments based on a review organization’s or the payer’s findings.
CO-193 when the review upholds the original decision.
CO-129 when prior processing appears incorrect.

If you still see CO-64

It will usually be in older payment history, often next to the original denial. When reconciling, match the reversal to the earlier denial so that any write-off you posted then is backed out and the payment is applied to the correct claim.

If you are tracking appeal outcomes, a CO-64 in historical data is a useful marker of a successful medical review.

CO-216 (Based on the findings of a review organization or the payer's findings.): An adjustment based on the findings of a review organization or the payer's own review.
CO-193 (Original payment decision is being maintained.): The opposite outcome: the original decision was maintained after review.
CO-129 (Prior processing information appears incorrect.): Prior processing information appears incorrect.

CO-64 FAQ

Was CO-64 a denial?

No. It signaled that a prior denial was reversed after the payer's medical reviewers looked at the claim again, typically resulting in payment.

How is a reversed denial shown today?

Payers usually reprocess the claim and send a new remittance with the payment. No specific adjustment code is required to say a denial was reversed.

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