CO-163CO group · Administrative

CO-163 denial code: required attachment or documentation not received

CO-163 is the code that punishes a document that was sent but not linked. Before resending anything, establish whether the payer has it under a different reference.

CO-163 fires when a claim requires supporting documentation and the payer's system has none attached. It can mean the document was never sent, or that it arrived without a reference that connected it to the claim.

What CO-163 means

Payers accept attachments through several channels — electronic attachment transactions, portal upload, fax cover sheets with a control number — and each depends on a reference tying the document to the claim. Where that reference is missing or mistyped, the document exists in the payer's records and the claim still denies for want of it. That distinction determines whether you resend or ask the payer to search.

Why CO-163 fires

  • The documentation was never submitted for a service that requires it.
  • An attachment was sent without the control number that links it to the claim.
  • The attachment arrived after the payer's adjudication window and was not matched.
  • The payer required a specific form and received a general clinical record instead.

Is CO-163 worth appealing?

Sometimes worth appealing

Establish what the payer holds before resending. Where the document was submitted correctly and the payer lost the linkage, that is worth saying in writing — a resend restarts a clock that should not have restarted.

How to resolve or appeal CO-163

  1. 1

    Find your proof of submission

    The attachment control number, portal confirmation or fax receipt with a timestamp.

  2. 2

    Resend with the linkage explicit

    Reference the claim number and the original submission date on the cover so the payer connects rather than re-dates it.

CO-163 — frequently asked

How do I know which document is wanted?
The remark code paired with CO-163 names it, and the payer's policy for that service usually enumerates it. Sending everything in the chart is slower and often triggers a second request.
Does resending restart the filing clock?
For the claim, usually not. For the documentation request, some payers set their own response window, and missing it converts a documentation problem into a timely-filing one.

Related guides

CO-252 · AdministrativeCO-251 · AdministrativeCO-16 · Administrative

Sources

Reason-code meanings are paraphrased from the X12 Claim Adjustment Reason Code list for plain-language reference; they are not reproduced verbatim. This is general information, not legal, coding, or medical advice — always confirm against the payer's remittance and policy.

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