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N251 Remark Code: Attending Provider Taxonomy Issue

N251 means the payer could not accept the taxonomy code reported for the attending provider. The specialty code was left off, was not a valid taxonomy value, or did not match what the payer has on file for that clinician.

Quick facts

Code
N251 (RARC N251)
Status
Active In use since December 2, 2004.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The service was denied or held because of a claim data error the facility can correct. The patient should not be billed for it.
Official description
Missing/incomplete/invalid attending provider taxonomy.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N251 means

On a hospital, skilled nursing, hospice, or other facility claim, the attending provider is the clinician primarily responsible for the patient’s care during the billed period. Some payers want that person’s specialty identified with a Health Care Provider Taxonomy code, a 10-character value from the national taxonomy code set. N251 says that value was absent, malformed, or not acceptable to the payer.

The remark usually rides alongside CARC 16, which tells you the claim has a data problem. N251 narrows that problem to one element, so you do not need to rework the charges, codes, or dates.

Common causes

  • The payer began requiring attending taxonomy and the facility’s billing system never populated it.
  • A taxonomy was typed with a transposed character or the wrong length.
  • The taxonomy describes a different specialty from the one on the physician’s NPPES record or payer enrollment file.
  • The claim carried a broad taxonomy (for example, a general internal medicine value) when the payer’s edit expected the physician’s actual subspecialty.
  • A hospitalist group changed attending physicians mid-stay and the claim reflected the wrong clinician’s specialty.

How to fix it

  1. Identify who was the attending physician for the dates on the claim, using the medical record.
  2. Look up that physician in the NPPES registry and note the primary taxonomy listed with the NPI.
  3. Compare it with the taxonomy your payer enrollment shows. If they differ, decide which one the payer expects before you resubmit.
  4. Update the attending provider information in your billing system so the correct taxonomy flows into the 837I.
  5. Send a corrected institutional claim using the replacement frequency code (7) and the original claim number, unless the payer’s policy says to submit a new claim.

How to prevent it

Keep a physician master file that stores each clinician’s NPI and taxonomy together, and refresh it when doctors join or update their NPPES entries. Build a front-end edit that stops institutional claims when a required attending taxonomy is blank. Our guide on provider enrollment denials covers how mismatched enrollment data drives remarks like this one.

Codes that may appear with N251

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): Claim lacks information or has a billing error; N251 points to the attending provider's taxonomy as the problem field.
  • CO-A1 (Claim/Service denied.): Some payers issue a general denial and rely on N251 to say which data element failed.
  • N253 (Missing/incomplete/invalid attending provider primary identifier.): Used when the attending provider's NPI, rather than the taxonomy, is missing or invalid.
  • N252 (Missing/incomplete/invalid attending provider name.): Used when the attending provider's name is missing or does not match.
  • N94 (Claim/Service denied because a more specific taxonomy code is required for adjudication.): Tells you a more specific taxonomy is required, rather than that the code is missing or invalid.
  • N255 (Missing/incomplete/invalid billing provider taxonomy.): The same taxonomy problem, but for the billing provider instead of the attending.

N251 FAQ

Where does the attending provider taxonomy go?

On an electronic 837I it is reported with the attending provider's details. The paper UB-04 has no dedicated attending taxonomy field, so payers that need it usually expect electronic submission or give their own paper instructions.

Which taxonomy should I use for the attending physician?

Use the taxonomy that describes the clinician's specialty for this stay and that matches their NPPES record and payer enrollment. A generic code can fail if the payer expects a more specific one.

Can N251 appear on a professional claim?

It is mainly an institutional-claim remark, because the attending provider role belongs to facility billing. Professional claims more often draw rendering or billing taxonomy remarks.