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M33 Remark Code (Deactivated): UPIN Missing or Invalid

M33 meant the UPIN for the ordering, referring, or performing provider was missing, incomplete, or invalid. X12 deactivated it and suggested M68, which has also been retired; provider identifiers are now NPIs, flagged with role-specific remarks such as N286 or N290.

X12 deactivated RARCM33 on August 1, 2004. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals.

Quick facts

Code
M33 (RARC M33)
Status
Deactivated StoppedAugust 1, 2004 (in use since January 1, 1997).
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): Usually accompanied CARC 16 under CO, since correct provider identifiers are the billing provider's responsibility.
Official description
Missing/incomplete/invalid UPIN for the ordering/referring/performing provider.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What M33 meant

Remark M33 told providers that a UPIN on the claim was absent or unusable. UPINs identified the physician who ordered, referred, or performed the service. When one of those numbers was blank or did not match Medicare’s records, the payer could not validate the claim and used this remark to explain the rejection.

What replaced it

X12’s note suggested M68, which covered attending, ordering, rendering, supervising, and referring physician identification in one remark. M68 was later retired too. Since the national move to NPIs, payers use remarks specific to each provider role, including N286 for the referring provider, N265 for the ordering provider, and N290 for the rendering provider.

If you still see M33

It only appears in archives from the UPIN era. If you are researching an old denial, the fix would have been to supply a valid UPIN for the provider named. For any current claim with a provider identifier remark, check the NPI for each role on the claim against the NPPES registry and the payer’s enrollment records, then correct and resubmit.

  • M68Deactivated (Missing/incomplete/invalid attending, ordering, rendering, supervising or referring physician identification.): The code X12 suggested instead, itself later deactivated.
  • N286 (Missing/incomplete/invalid referring provider primary identifier.): Missing, incomplete, or invalid referring provider primary identifier.
  • N265 (Missing/incomplete/invalid ordering provider primary identifier.): Missing, incomplete, or invalid ordering provider primary identifier.
  • N290 (Missing/incomplete/invalid rendering provider primary identifier.): Missing, incomplete, or invalid rendering provider primary identifier.

M33 FAQ

What was a UPIN?

The Unique Physician Identification Number, an identifier Medicare assigned to physicians and some other practitioners before the National Provider Identifier replaced it.

Is there any reason to report a UPIN today?

No. Claims use the NPI for ordering, referring, and rendering providers. An old claim denied under M33 would need the correct provider identifier for its era.