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M21 Remark Code: Home Residence Information Invalid

M21 means the payer could not confirm where the patient lives for a service or item provided in the home, because the place of residence on the claim is missing, incomplete, or invalid.

Quick facts

Code
M21 (RARC M21)
Status
Active In use since January 1, 1997; last modified February 28, 2003.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The line is unpaid until residence information is corrected. It is not billed to the patient.
Official description
Missing/incomplete/invalid place of residence for this service/item provided in a home.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What M21 means

Services and items furnished in the patient’s home, such as home visits and home-use equipment, depend on the payer knowing where that home is. M21 says the residence information was missing or did not make sense. The payer cannot confirm that the service happened in a qualifying home setting, and in the case of DME it may not be able to route the claim to the right jurisdiction.

Common causes

  • The patient address is blank, incomplete, or uses a P.O. box where a street address is required.
  • The place of service code does not match a home setting.
  • The service location differs from the patient’s address and was not reported.
  • The address on the claim does not match the payer’s records after a recent move.

How to fix it

  1. Confirm the patient’s current residence and street address.
  2. Correct the address fields and the place of service code in box 24B.
  3. Add the service location if the payer requires it for home services.
  4. Resubmit as a new claim if it was returned as unprocessable, or as a corrected claim with resubmission code 7 otherwise.

How to prevent it

Verify addresses at each order or home visit and require a street address for home-based services. Mismatched demographics are a common source of front-end errors; see the CO-16 guide.

Codes that may appear with M21

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): The claim lacks information needed to adjudicate the home service.
  • CO-5 (The procedure code/type of bill is inconsistent with the place of service.): The place of service is inconsistent with the service billed.
  • M18 (Certain services may be approved for home use.): The patient was in a hospital or SNF, which does not count as the home.
  • M11 (DME, orthotics and prosthetics must be billed to the DME carrier who services the patient's zip code.): DME must go to the contractor for the patient's ZIP code, which also depends on the address.
  • CO-58 (Treatment was deemed by the payer to have been rendered in an inappropriate or invalid place of service.): Treatment rendered in an inappropriate or invalid place of service.

M21 FAQ

Which fields carry residence information?

The patient's address (box 5 on the CMS-1500) and the place of service in box 24B. Some home services also require a service facility or residence address.

Does an assisted living facility count as a home?

Often yes for many benefits, but it depends on the payer and the benefit. Use the place of service code that matches the actual setting.

Is M21 an appealable denial?

It is a data problem. Correcting the address or place of service is faster than an appeal.