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M42 Remark Code: Physician Must Sign Necessity Form

M42 means the payer rejected the medical necessity form because the attending physician did not personally sign it. A signature by staff, a stamp, or a missing signature does not meet the requirement.

Quick facts

Code
M42 (RARC M42)
Status
Active In use since January 1, 1997.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The supplier or provider absorbs the amount until a properly signed form is submitted.
Official description
The medical necessity form must be personally signed by the attending physician.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What M42 means

Medical necessity forms, such as certificates of medical necessity for equipment or other attestation forms, are only valid when the right person signs them. M42 says the attending physician did not personally sign this one. That leaves the payer without proof that the treating physician supports the service.

This remark is Medicare-rooted and is often seen on durable medical equipment claims.

Common causes

  • Office staff or the supplier signed on the physician’s behalf.
  • A rubber stamp was used in place of a signature.
  • The form was signed by a practitioner other than the attending physician.
  • The signature line was left blank or the signature was illegible without a signature log.
  • An electronic signature did not meet the payer’s standards.

How to fix it

  1. Return the form to the attending physician for a personal signature and date.
  2. Include a signature log or attestation if the payer allows it for illegible signatures.
  3. Resubmit the form through the payer’s documentation process and resubmit the claim if required, using resubmission code 7 for a corrected claim.
  4. Recheck other months billed with the same defective form.

How to prevent it

Review every medical necessity form for a compliant physician signature before billing, and educate referring offices on signature rules. Pre-submission checks, including the Claims Validator, help catch missing documentation fields. See the CO-16 guide.

Codes that may appear with M42

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): Required information, a valid physician signature, is missing.
  • CO-50 (These are non-covered services because this is not deemed a 'medical necessity' by the payer.): Without a valid form, medical necessity is not established.
  • CO-252 (An attachment/other documentation is required to adjudicate this claim/service.): Documentation must be supplied before the claim can be processed.
  • M19 (Missing oxygen certification/re-certification.): The oxygen certification is missing entirely.
  • MA81 (Missing/incomplete/invalid provider/supplier signature.): The provider or supplier signature on the claim itself is missing or invalid.
  • N234 (Incomplete/invalid oxygen certification/re-certification.): The oxygen certification is incomplete or invalid.

M42 FAQ

Are signature stamps acceptable?

Medicare generally does not accept rubber-stamped signatures on medical documentation. Handwritten and compliant electronic signatures are acceptable.

Can a nurse practitioner or physician assistant sign?

It depends on the form and the payer. Some forms allow other treating practitioners; M42 specifically says this form needed the attending physician.

Can the physician sign the form after the fact?

Payers have rules about late signatures and attestations. Check the payer's signature policy before relying on a late signature.