CO-164 denial code
Attachment or documentation was not received in a timely fashion
How to fix it
Check whether a further appeal level remains. Submit immediately with proof of the original send where available.
How to prevent it
Track documentation deadlines on the same list as filing deadlines.
The CO prefix marks this a contractual obligation. The balance is absorbed by the provider under the payer agreement and cannot be transferred to the patient.
In practice
A payer requests records with a thirty-day response window. The request is routed to a clinical inbox nobody monitors and surfaces at day forty-five. The documents are sent and the claim returns CO-164.
The documentation itself was adequate. What failed is that it arrived after the window closed, and the payer treats a late response as no response.
Where the original send was timely and only receipt is disputed, transmission confirmation supports an appeal. Where the response genuinely was late, the remaining question is whether a further appeal level exists, and often it does not.
What sits behind it
Documentation deadlines are shorter than filing deadlines and start from the request date, which means they can expire while a claim is otherwise well within time. They also arrive unpredictably, which makes them harder to plan around than a known filing window.
The routing failure is the usual root cause. Payer requests arrive by post, portal message or electronic transaction, and where no single person owns the inbox, requests sit unread. Central logging with an owner and a due date is the control that prevents this category.
Because the loss is procedural rather than substantive, these denials are particularly worth preventing. The underlying claim was frequently payable, and the documentation existed the whole time; only the calendar defeated it.
Related codes
Terms used here — Timely Filing · Appeal · Denial
How we handle it — Denial Management · AR Management · Practice Analytics
Primary sources
The rules behind CO-164, at the bodies that publish them.
- Medicare timely filing requirements (opens in a new tab)
Centers for Medicare & Medicaid Services — The one-year filing limit and the narrow exceptions to it. Commercial payers set their own, usually shorter, limits by contract.
- 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.
- 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.
Looking for a different code? Search all 190 CARC and RARC codes
Questions about CO-164
Commonly thirty to forty-five days from the request date, though it varies by payer and by review type. The window is shorter than the filing deadline and starts when the request is issued, so it can expire on a claim that is otherwise comfortably in time.
Where you can show the original send was timely and only receipt is in dispute, transmission confirmation supports the appeal. Where the response was genuinely late, the question is whether a further appeal level remains, and frequently none does.
Log every payer request centrally with an owner and a due date, regardless of how it arrived. The usual root cause is a request landing in an inbox nobody monitors, and no amount of individual diligence fixes a routing problem.
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