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M66 Remark Code: Bill Technical and Professional Separately

M66 means you billed a diagnostic test that is subject to price limitations as a global service. Only the technical component is subject to the limit, so the payer needs the technical and professional components on separate lines.

Quick facts

Code
M66 (RARC M66)
Status
Active In use since January 1, 1997.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The line is unpaid as billed. Rebilling the components separately is needed; the patient is not billed.
Official description
Our records indicate that you billed diagnostic tests subject to price limitations and the procedure code submitted includes a professional component. Only the technical component is subject to price limitations. Please submit the technical and professional components of this service as separate line items.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What M66 means

Many diagnostic tests have a technical component (the equipment and staff performing the test) and a professional component (the physician’s interpretation). When the technical part is a purchased test, Medicare limits payment for that part. If you bill the whole service as one global line, the payer cannot apply the limit to the technical part alone. M66 asks you to split the service into two lines.

It is a Medicare remark tied to purchased diagnostic test pricing.

Common causes

  • A purchased test was billed as a global service with no component modifier.
  • The billing system defaults all diagnostic tests to global billing.
  • The practice did not flag which tests were purchased from outside suppliers.

How to fix it

  1. Confirm the technical component was purchased and gather the purchase price and supplier details.
  2. Split the service into a TC line and a 26 line in box 24D.
  3. Report purchased-service information for the TC line and the interpreting physician for the 26 line.
  4. Resubmit as a corrected claim with resubmission code 7 or a new claim, as the payer directs.

How to prevent it

Flag purchased tests at order entry so the billing system automatically splits components. The Claims Validator can catch global billing on tests marked as purchased. For more on modifier-driven denials, see NCCI bundling and modifiers.

Codes that may appear with M66

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): The claim contains billing errors in how the service was reported.
  • CO-4 (The procedure code is inconsistent with the modifier used.): The code is inconsistent with the modifiers used, or the component modifiers are missing.
  • N184 (Rebill technical and professional components separately.): A general instruction to rebill technical and professional components separately.
  • N13 (Payment based on professional/technical component modifier(s).): Payment was based on the component modifiers reported.
  • M12 (Diagnostic tests performed by a physician must indicate whether purchased services are included on the claim.): The claim did not state whether purchased services were included.

M66 FAQ

Which modifiers identify the components?

Modifier TC identifies the technical component and modifier 26 identifies the professional component. The global service is billed without either.

Why do price limits apply only to the technical component?

Limits on purchased diagnostic tests apply to the technical work bought from a supplier. The professional interpretation is paid under the regular fee schedule.

Do I need two claims or two lines?

M66 asks for separate line items. Put the TC line and the 26 line on the claim with the correct providers and purchased-service details.