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M133 Remark Code: Purchased Test Details Missing

M133 means the claim for a purchased diagnostic test did not identify who performed the test, or the amount you were charged for it. Payers need both to apply purchased-test pricing rules.

Quick facts

Code
M133 (RARC M133)
Status
Active In use since January 1, 1997.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The test was not paid due to missing information. The billing provider corrects and resubmits; the patient is not billed.
Official description
Claim did not identify who performed the purchased diagnostic test or the amount you were charged for the test.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What M133 means

A physician or group can sometimes bill for a diagnostic test performed by an outside supplier, called a purchased test. Payers that allow this, such as Medicare, apply special rules. They need to know who performed the test and what the billing provider paid for it, because payment may be limited by that purchase price.

M133 tells you one or both were missing. Without them, the payer cannot apply its purchased-test rules and rejects the line.

Common causes

  • Box 20 (outside lab or purchased service) left unchecked or without the charge amount.
  • The performing supplier’s name, address, or NPI missing in box 32 and 32a or the electronic purchased-service fields.
  • A billing system that treats the purchased test like an in-house test.
  • Invoices from the supplier not received before billing, so the amount is unknown.

How to fix it

  1. Get the supplier’s invoice and details, including the NPI and service location.
  2. Complete the purchased-service fields: the purchased indicator, the amount charged to you, and the performing supplier’s information.
  3. Confirm the test is billable as purchased under the payer’s rules.
  4. Resubmit, using frequency code 7 if the original claim was adjudicated.

How to prevent it

  • Flag purchased tests in your charge master so claims automatically include the required fields.
  • Keep supplier NPIs and addresses on file.
  • Wait for the supplier’s invoice before billing, or record the agreed price in advance.
  • Run a Claims Validator check that purchased-service fields are complete.

Codes that may appear with M133

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): The claim lacks information, identified by M133 as the purchased test details.
  • MA114 (Missing/incomplete/invalid information on where the services were furnished.): Information about where services were furnished was missing or invalid.
  • M96 (The technical component of a service furnished to an inpatient may only be billed by that inpatient facility.): The technical component for an inpatient must be billed by the facility.

M133 FAQ

What is a purchased diagnostic test?

A test, usually the technical component, that the billing provider buys from an outside supplier and then bills to the payer, under the payer's purchased-service rules.

Where do I report the details on a CMS-1500?

Box 20 indicates an outside or purchased service and the amount charged, and box 32 and 32a identify the performing supplier's location and NPI. Electronic claims have equivalent fields.

Why does the charge matter?

Medicare and some other payers limit payment for a purchased test to the lower of certain amounts, including what the billing provider paid for it.