CO-163 denial code
Attachment or other documentation referenced on the claim was not received
How to fix it
Resend the attachment through the payer's required channel and reference the claim number.
How to prevent it
Confirm the payer's accepted attachment method. Faxed records to a payer expecting electronic attachments are treated as never sent.
In practice
A practice faxes operative notes in support of a claim that references them. The payer returns CO-163, stating the attachment was not received, and the practice faxes again with the same result.
The payer required attachments through its electronic channel. Faxed records to a payer expecting an electronic submission are frequently treated as though they never arrived, because they never reach the queue linked to the claim.
Establishing the payer's accepted method before resending is the whole of the fix. Once sent through the right channel with the claim number referenced, the same documents that failed twice by fax are received without difficulty.
What sits behind it
Attachment handling varies more between payers than almost any other process. Some accept electronic attachments through a standard transaction, some require upload through a portal, some still take fax to a dedicated number, and some require a paper cover sheet with a specific control number.
Referencing matters as much as routing. Documents arriving without the claim number, patient identifier and date of service often cannot be matched to the claim even when they reach the right department, and unmatched documents are functionally lost.
Because the deadline continues to run while documents bounce, this code converts into CO-164 with alarming ease. Confirming receipt rather than assuming it, and keeping the transmission confirmation, is what preserves the appeal if the deadline does pass.
Related codes
Terms used here — Appeal · Timely Filing · Clearinghouse
How we handle it — Denial Management · Claims Management · AR Management
Primary sources
The rules behind CO-163, at the bodies that publish them.
- Evaluation and Management services guide (opens in a new tab)
Centers for Medicare & Medicaid Services — How E/M level is determined under the current medical decision making and time rules. The reference for any dispute about whether documentation supports a level.
- Medicare Claims Processing Manual (opens in a new tab)
Centers for Medicare & Medicaid Services — The operative manual for how Medicare claims must be coded, submitted, adjusted and appealed. When a payer policy and a vendor's advice disagree, this settles it.
- Medicare claims appeals process (opens in a new tab)
Centers for Medicare & Medicaid Services — The five levels of appeal, what each requires and the deadline for each. Missing a level's deadline ends the appeal regardless of the claim's merits.
Looking for a different code? Search all 190 CARC and RARC codes
Questions about CO-163
Because many payers now require attachments through an electronic channel or portal, and faxed documents never reach the queue linked to the claim. Confirm the accepted method before resending, or the second attempt fails exactly as the first did.
The claim number, patient identifier and date of service, in whatever format the payer specifies. Documents that arrive without them frequently cannot be matched to the claim even when they reach the correct department, which makes them functionally lost.
Keep every transmission confirmation, because proof of the original send is what supports an appeal once this converts into a timeliness denial. Confirming receipt rather than assuming it is the practice that prevents the conversion in the first place.
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