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N450 Remark Code: Primary Treating Physician Only

N450 means the service is covered only when performed by the primary treating physician or that physician's designee. The provider on the claim was not recognized as the primary treating physician or as someone the treating physician designated.

Quick facts

Code
N450 (RARC N450)
Status
Active In use since July 1, 2008.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The payer denied the service because of who performed it. The provider generally cannot bill the patient, particularly in workers' compensation.
Official description
Covered only when performed by the primary treating physician or the designee.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N450 means

Certain services are tied to a specific role: the physician in charge of the patient’s care for the condition. N450 says the payer pays for this service only when that primary treating physician, or someone they designated, performs it. The provider on the claim was not in that role according to the payer’s records. It commonly accompanies CARC 170 or CARC 185.

The concept is especially common in workers’ compensation, where one physician coordinates treatment, work status, and reporting for an injured worker.

Common causes

  • The patient saw a different provider than the one on file as the primary treating physician.
  • A referral or designation existed but was not documented to the carrier.
  • The patient changed treating physicians, and the carrier’s records were not updated.
  • The claim listed the wrong rendering provider, such as a colleague instead of the designated treating physician.

What to do

  1. Check who the carrier lists as the primary treating physician for the claim, and the effective date.
  2. Verify the rendering provider on the claim, in CMS-1500 box 24J. If it was wrong, correct it and send a corrected claim with resubmission code 7.
  3. Provide the designation or referral if the treating physician referred the patient to your provider.
  4. Document a change if the patient properly switched treating physicians, following the jurisdiction’s procedures.
  5. Appeal with the documentation if the carrier’s records are out of date.

How to prevent it

For workers’ compensation patients, confirm the primary treating physician with the adjuster before the first visit. If you are receiving a referral, get the referral in writing and send it with your first claim. Record the treating physician in the patient account so every claim lists the right provider.

Codes that may appear with N450

  • CO-170 (Payment is denied when performed/billed by this type of provider.): Payment is denied when performed or billed by this type of provider.
  • CO-185 (The rendering provider is not eligible to perform the service billed.): The rendering provider is not eligible to perform the service billed.
  • CO-P17 (Referral not authorized by attending physician per regulatory requirement.): A referral was not authorized by the attending physician as required by regulation.
  • N95 (This provider type/provider specialty may not bill this service.): The provider type or specialty may not bill this service.
  • CO-243 (Services not authorized by network/primary care providers.): Services not authorized by network or primary care providers.
  • CO-P16 (Medical provider not authorized/certified to provide treatment to injured workers in this jurisdiction.): The provider is not authorized or certified to treat injured workers in the jurisdiction.

N450 FAQ

Where does the primary treating physician concept come from?

It is common in workers' compensation, where one physician is responsible for managing the injured worker's care and reports. Some health plans use similar gatekeeper rules.

What is a designee?

A provider the primary treating physician has referred the patient to or authorized to perform services. The designation usually needs to be documented.

What if our physician became the primary treating physician later?

Send documentation of the change, including the effective date, to the carrier and ask it to reprocess services from that date forward.