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N666 Remark Code: One E/M at This Level per Course of Care

N666 means the payer covers only one evaluation and management (E/M) service at this level during a course of care, and one was already billed. Later visits in the same episode are expected to be billed at a different level or as a different type of service.

Quick facts

Code
N666 (RARC N666)
Status
Active In use since July 15, 2013.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The repeated visit at that level is denied as a billing issue. The provider absorbs it, and it generally should not be billed to the patient.
Official description
Only one evaluation and management code at this service level is covered during the course of care.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N666 means

Some payers, and some state fee schedules for injury care, limit how often a provider can bill the same level of evaluation and management service within a single episode of treatment. The idea is that a full evaluation happens at the start, while later visits are shorter re-evaluations or treatment visits.

N666 tells you the payer already paid an E/M service at this level for the current course of care and won’t pay a second one at the same level. It often comes with CARC 151 or 119.

Common causes

  • Every visit in a treatment plan was billed at the same E/M level as the initial evaluation.
  • A re-evaluation was coded at the initial-visit level instead of the level the notes support.
  • An E/M visit was billed alongside each treatment session, when the payer expects E/M only when a separate evaluation happens.
  • The payer treated a new condition as part of the old course of care because the claim didn’t show a new diagnosis or injury.

How to fix it

  1. Review the patient’s claim history to find the earlier E/M at the same level.
  2. Check the documentation for the denied visit and determine the level and type of service it actually supports.
  3. Send a corrected claim with resubmission code 7 in box 22 if the visit should have been coded differently.
  4. Appeal if the visit began a new course of care, such as for a new condition, with documentation and diagnoses in box 21 that show it.
  5. Add modifier 25 only when appropriate, meaning a significant, separately identifiable E/M service on the same day as a procedure, and only when the documentation supports it.

How to prevent it

Set up visit templates so ongoing treatment visits don’t default to the initial evaluation level. When a patient starts care for a new problem, document it as a new episode with its own diagnosis so the payer can distinguish it from the earlier one.

Codes that may appear with N666

  • CO-151 (Payment adjusted because the payer deems the information submitted does not support this many/frequency of services.): The information submitted does not support this many services or this frequency.
  • PR-119 (Benefit maximum for this time period or occurrence has been reached.): The benefit maximum for the period or occurrence has been reached.
  • N637 (Consultations are not allowed once treatment has been rendered by the same provider.): A consultation billed after the same provider has already started treatment.
  • N636 (Adjusted because this is reimbursable only once per injury.): A service reimbursable only once per injury.
  • N626 (New or established patient E/M codes are not payable with chiropractic care codes.): New or established patient visits are not payable with chiropractic care codes.
  • CO-150 (Payer deems the information submitted does not support this level of service.): The level of service billed isn't supported by the documentation.

N666 FAQ

What counts as a course of care?

It is the episode of treatment for a condition, as the payer or fee schedule defines it. The definition varies, and in workers' compensation it may be tied to the injury claim.

Does N666 mean I cannot bill any more visits?

No. It restricts repeating the same level of E/M service. Later visits may be payable when billed at the level the documentation supports or as the appropriate follow-up service.

Is N666 common with chiropractic and therapy care?

It can show up where a course of treatment involves many visits, such as chiropractic, physical therapy, or injury care, and the payer limits evaluation visits within it. The rules vary by payer and state.