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CO-D18 Denial Code (Deactivated): Missing Diagnosis Info

CO-D18 meant the claim or service was missing diagnosis information. X12 deactivated it and its notes say to use CARC 16 with the appropriate remark code, such as M76.

X12 deactivated CARCD18 on June 30, 2007. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals.

Code: CO-D18 (CARC D18)
Status: Deactivated StoppedJune 30, 2007 (in use since January 1, 1995).
Code set: Claim Adjustment Reason Codes (CARC)
Group codes: CO (Contractual Obligation): Diagnosis reporting was the provider's responsibility, so the patient was not billed.
Official description: Claim/Service has missing diagnosis information.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What CO-D18 meant

CARC D18 was used when diagnosis information the payer needed was not on the claim or service line. Payers cannot judge coverage or medical necessity without a diagnosis, so the claim was returned as incomplete.

What replaced it

X12’s note says to use code 16 with the appropriate remark code. Today the usual combination is CO-16 with remark M76, which covers a missing, incomplete, or invalid diagnosis or condition. When a diagnosis is present but not valid for the service date, payers use CO-146.

If you still see CO-D18

You will only find it in older remittances. For a current missing-diagnosis denial, check each service line’s diagnosis pointers, confirm required diagnosis positions are filled, and verify the codes are complete to the required number of characters. Fix the claim and resubmit it as a corrected claim.

CO-16 (Claim/service lacks information or has submission/billing error(s).): Named replacement: claim lacks information, with a remark code.
M76 (Missing/incomplete/invalid diagnosis or condition.): Remark code for a missing, incomplete, or invalid diagnosis or condition.
CO-146 (Diagnosis was invalid for the date(s) of service reported.): Diagnosis was invalid for the date of service reported.

CO-D18 FAQ

How can a diagnosis be missing if the claim has one?

A service line may not point to any diagnosis, the pointer may reference an empty position, or a required diagnosis such as an external cause or principal diagnosis may be absent.

What distinguishes D18 from D21?

D18 described missing diagnosis information for a claim or service. D21 described diagnoses that were missing or invalid. Both were retired in favor of more general codes.

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