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M22 Remark Code: Mileage Missing or Invalid

M22 means the claim did not report a valid number of miles traveled. The payer needs the mileage to price the transport or travel-related charge, so the line cannot be paid as submitted.

Quick facts

Code
M22 (RARC M22)
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 mileage line is unpaid until corrected. It is a provider data issue and not billed to the patient.
Official description
Missing/incomplete/invalid number of miles traveled.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What M22 means

Mileage is billed as units, and the payer multiplies those units by its per-mile rate. M22 appears when the miles are missing, zero, unreadable, or out of line with the service. It is most common on ambulance claims but can also apply to other services that include a travel component.

The paired reason code is typically CARC 16. The claim may be returned as unprocessable, in which case a new claim is needed.

Common causes

  • The mileage line was billed with blank or zero units.
  • Fractional mileage was reported in a format the payer does not accept.
  • Total trip miles were reported instead of loaded miles only.
  • The base rate and mileage lines have mismatched dates or modifiers.
  • Pickup and destination details were missing, so the payer could not validate the distance.

How to fix it

  1. Pull the trip report and confirm the loaded mileage.
  2. Report the miles as units in box 24G, using the payer’s required precision.
  3. Match the mileage line to the base transport line: same date, same origin and destination modifiers.
  4. Resubmit as a corrected claim (resubmission code 7) or new claim, depending on how the payer returned it.

How to prevent it

Build a hard stop so a mileage line cannot leave your system with zero units, and pull mileage directly from the electronic patient care record. For more on unit errors in general, see MUE and units of service denials.

Codes that may appear with M22

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): The claim lacks information needed for adjudication, here the mileage.
  • CO-252 (An attachment/other documentation is required to adjudicate this claim/service.): Some payers ask for the trip record or other documentation to validate the miles.
  • N159 (Payment denied/reduced because mileage is not covered when the patient is not in the ambulance.): Mileage was denied or reduced because the patient was not in the ambulance.
  • N362 (The number of Days or Units of Service exceeds our acceptable maximum.): The units of service exceed the payer's acceptable maximum.
  • CO-16 (Claim/service lacks information or has submission/billing error(s).): The general missing-information reason code that usually carries M22.

M22 FAQ

How is ambulance mileage reported?

As units of the mileage HCPCS Level II code in box 24G, counting loaded miles with the patient on board. Medicare requires fractional mileage to the tenth of a mile for trips under 100 miles.

What if the mileage was zero?

If no loaded miles apply, do not bill a mileage line. A mileage line with zero or blank units will trigger M22.

Can I estimate mileage?

Mileage should come from the trip record, such as odometer readings or a mapping tool, and must be supported by documentation.