CO-207 denial code
National Provider Identifier invalid format
How to fix it
Correct the NPI. A valid NPI is ten digits and passes a check-digit test.
How to prevent it
Apply NPI format validation at entry so invalid numbers cannot be saved.
In practice
A claim is submitted with a referring provider identifier transcribed from a handwritten order. One digit was misread, and the number fails the check digit test, returning CO-207.
A valid identifier is ten digits and carries a check digit calculated from the preceding nine. A transposition or a misread character breaks that arithmetic and the number is rejected as malformed before any lookup occurs.
Correcting the identifier resolves it, and the underlying prevention is validating format at the point of entry so a malformed number cannot be saved in the first place.
What sits behind it
The distinction between this and a mismatch matters for the fix. CO-207 means the number is not a valid identifier at all; CO-208 means it is valid but does not match the payer's record for that provider. The first is arithmetic, the second is enrolment.
Because the check digit calculation is public and deterministic, format validation can run entirely offline at data entry. Any system storing provider identifiers can reject an invalid one immediately rather than carrying it into a claim weeks later.
Handwritten orders remain the main source. A number transcribed from paper is exposed to misreading in a way an electronically transmitted one is not, which is a further argument for capturing identifiers electronically wherever referral sources can support it.
Related codes
Terms used here — NPI · Clean Claim · Claim Scrubbing
How we handle it — Claims Management · Provider Credentialing · Medical Billing & Coding
Primary sources
The rules behind CO-207, at the bodies that publish them.
- Remittance Advice Remark Codes (RARC) (opens in a new tab)
X12 — The remark codes that qualify a CARC on an ERA. Reading the RARC is usually what tells you whether a denial is appealable.
- CMS-1500 claim form standards (opens in a new tab)
National Uniform Claim Committee — Maintainer of the CMS-1500 professional claim form and its data element definitions, plus the provider taxonomy code set.
- NPI Registry (NPPES) (opens in a new tab)
Centers for Medicare & Medicaid Services — Public lookup and management for National Provider Identifiers. A stale NPPES record is a quietly common cause of enrollment and claim rejections.
Looking for a different code? Search all 190 CARC and RARC codes
Questions about CO-207
It must be ten digits and pass a check digit calculation performed on the first nine. The algorithm is public and deterministic, which means validation can run offline at the point of entry rather than waiting for a payer to reject the claim.
CO-207 means the number is not a well-formed identifier — it fails the arithmetic. CO-208 means it is well-formed and real but does not match the payer's record for that provider, which is an enrolment problem rather than a data entry one.
Transcription from handwritten orders, where a misread or transposed digit is easy and invisible. Capturing identifiers electronically from referral sources removes the transcription step that creates the error.
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