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CO-D23 Denial Code (Deactivated): Dual Eligible, Part D

CO-D23 meant a dual eligible patient was covered by Medicare Part D, based on retroactive Medicare eligibility, so the claim belonged with the Part D plan. X12 deactivated it without naming a replacement; a remark code was required to give specifics.

X12 deactivated CARCD23 on January 1, 2012. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals.

Quick facts

Code
CO-D23 (CARC D23)
Status
Deactivated StoppedJanuary 1, 2012 (in use since November 1, 2009).
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The paying program did not cover the claim; the pharmacy or provider needed to bill Part D.
Official description
This dual eligible patient is covered by Medicare Part D per Medicare Retro-Eligibility. At least one Remark Code must be provided (may be comprised of either the NCPDP Reject Reason Code, or Remittance Advice Remark Code that is not an ALERT.)
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-D23 meant

CARC D23 dealt with patients who have both Medicare and Medicaid. When Medicare eligibility was established retroactively, the patient’s drug coverage for that period shifted to Medicare Part D. This code told the provider, usually a pharmacy, that the claim should be handled by Part D instead, with a required remark code giving the details.

What replaced it

X12 did not name a successor. Similar situations are now reported with general coordination codes such as CO-109, meaning the claim is not covered by this payer, or OA-22 when another payer may be responsible. Remark N751 indicates the patient is covered under a Medicare Part D plan.

If you still see CO-D23

It should only turn up in older data. For a current claim affected by retroactive Medicare eligibility, identify the patient’s Part D plan for the date of service, submit to it, and follow the reversal instructions of the program that originally paid. Keep records of the eligibility change in case of later audits.

  • CO-109 (Claim/service not covered by this payer/contractor.): Claim not covered by this payer; send it to the correct payer.
  • OA-22 (This care may be covered by another payer per coordination of benefits.): This care may be covered by another payer per coordination of benefits.
  • N751 (Adjusted because the patient is covered under a Medicare Part D plan.): Remark code: adjusted because the patient is covered under a Medicare Part D plan.

CO-D23 FAQ

What is a dual eligible patient?

Someone enrolled in both Medicare and Medicaid. For most prescription drugs, Medicare Part D pays before Medicaid.

What does retroactive eligibility change?

When Medicare eligibility is established back to an earlier date, drug claims that another program already paid may need to be reprocessed under the Part D plan for that period.