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M31 Remark Code: Radiology Report Missing

M31 means a radiology report was needed to process this claim and was not received. The payer will not pay the line until the imaging report is provided.

Code: M31 (RARC M31)
Status: Active In use since January 1, 1997; last modified August 1, 2004.
Code set: Remittance Advice Remark Codes (RARC)
Group codes: CO (Contractual Obligation): The unpaid line is a provider documentation issue and is not billed to the patient.
Official description: Missing radiology report.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What M31 means

A radiology report documents what an imaging study showed and who interpreted it. M31 says the payer needed that report to process your claim. It may be supporting the imaging service itself, or another service whose coverage depends on imaging findings, such as a procedure that requires evidence of a condition.

It usually pairs with CARC 16, 252, or 226 and is often resolved by sending the report rather than appealing.

Common causes

A records request was not answered in time.
The imaging was performed elsewhere and the billing provider did not have the report.
An unlisted imaging code was billed without supporting documentation.
The attachment lacked claim identifiers or went to the wrong address.

How to fix it

Obtain the signed radiology report from the interpreting radiologist or imaging facility.
Send it to the payer using its attachment method, clearly referencing the claim.
Resubmit if needed with resubmission code 7 when the payer requires a corrected claim.
Track the claim until it reprocesses.

How to prevent it

Build a checklist of services for which each payer requires imaging support, and attach reports before submission. Faster responses to records requests keep M31 from becoming a final denial; see claim rejection vs denial for how pending and denied claims differ.

Codes that may appear with M31

CO-16 (Claim/service lacks information or has submission/billing error(s).): The claim is missing information required for adjudication.
CO-252 (An attachment/other documentation is required to adjudicate this claim/service.): An attachment is required to process the service.
CO-226 (Information requested from the Billing/Rendering Provider was not provided or not provided timely or was insufficient/incomplete.): Requested information was not provided or was insufficient.

N240 (Incomplete/invalid radiology report.): The radiology report was received but is incomplete or invalid.
M30 (Missing pathology report.): The pathology report is missing.
M1 (X-ray not taken within the past 12 months or near enough to the start of treatment.): An x-ray used to support chiropractic treatment was too old.

M31 FAQ

Which claims typically need a radiology report?

Imaging billed with an unlisted code, procedures where imaging supports medical necessity (for example some chiropractic or orthopedic services), and claims under medical review.

Is the image itself required?

M31 refers to the report, the radiologist's written interpretation. Some payers may ask for images separately, but the report is usually what is needed.

Can the interpreting radiologist's claim be affected?

Yes. The interpretation claim can be denied if the payer cannot confirm a report exists.

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