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M13 Remark Code: One Initial Visit per Specialty

M13 means the payer only covers one initial (new patient) visit per specialty within a medical group. Because another provider of the same specialty in the group already saw the patient, this visit should be billed as an established patient visit.

Quick facts

Code
M13 (RARC M13)
Status
Active In use since January 1, 1997; last modified June 30, 2007.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The difference is a provider write-off. The patient is not responsible for the new-patient level that was not covered.
Official description
Only one initial visit is covered per specialty per medical group.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What M13 means

Evaluation and management services come in new patient and established patient versions, and new patient visits pay more. M13 tells you the payer’s history shows the patient was already seen by someone of the same specialty in your medical group, so the new patient visit is not covered. It is a Medicare-rooted remark used by other payers too.

The rule is group-wide. If Dr. A saw the patient last year and Dr. B in the same group and specialty sees them today, Dr. B’s visit is established, even if it is their first meeting.

Common causes

  • A new provider joined the group and billed their first visit with an existing patient as new.
  • Providers in the group share a tax ID but the front desk looked only at the individual provider’s history.
  • Specialty enrollment for two providers is the same in the payer’s records, even though they practice differently.
  • A prior visit was within the payer’s look-back period.

How to fix it

  1. Check the patient’s history across all providers of the same specialty in the group.
  2. If an earlier visit exists within the look-back period, submit a corrected claim with resubmission code 7 and the established-patient visit level in box 24D.
  3. If the prior provider is a different specialty, verify the enrolled specialties with the payer and request reprocessing with evidence.
  4. If the prior visit was outside the look-back period, appeal with the visit dates.

How to prevent it

Search patient history by group and specialty, not just by rendering provider, before selecting a new patient visit. Keep payer specialty enrollment current for each provider; see provider enrollment denials.

Codes that may appear with M13

  • CO-4 (The procedure code is inconsistent with the modifier used.): The procedure code is inconsistent with the patient's status in the group.
  • OA-18 (Exact duplicate claim/service (Use only with Group Code OA except where state workers' compensation regulations requires CO)): An initial visit was already paid for this specialty in the group.
  • CO-151 (Payment adjusted because the payer deems the information submitted does not support this many/frequency of services.): The payer's information does not support this many initial services.
  • N113 (Only one initial visit is covered per physician, group practice or provider.): Only one initial visit per physician, group practice, or provider, a broader version of the same rule.
  • 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.
  • OA-18 (Exact duplicate claim/service (Use only with Group Code OA except where state workers' compensation regulations requires CO)): The general duplicate reason code that sometimes accompanies initial visit denials.

M13 FAQ

How does the payer define a new patient?

Medicare treats a patient as new if they have not received professional services from the same physician or another physician of the same specialty and subspecialty in the same group within the past three years. Other payers may define it differently.

Can a different specialty in the same group bill a new patient visit?

Generally yes, if the specialty is truly different. Make sure the provider's enrolled specialty matches.

Should I appeal M13?

Usually a corrected claim with the established-patient level is faster. Appeal only if the prior visit was by a different specialty or outside the look-back period.