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M2 Remark Code: Not Paid Separately for Inpatients

M2 means the payer will not pay the service separately because the patient was a hospital inpatient on that date. The service is considered part of the inpatient stay and is paid, if at all, through the facility's inpatient payment.

Code: M2 (RARC M2)
Status: Active In use since January 1, 1997.
Code set: Remittance Advice Remark Codes (RARC)
Group codes: CO (Contractual Obligation): The amount is a provider write-off because payment is included in the inpatient facility payment. It is not billable to the patient.
OA (Other Adjustment): Some payers use OA to show the line was simply rolled into the inpatient claim with no separate liability assigned.
Official description: Not paid separately when the patient is an inpatient.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What M2 means

When a patient is admitted as a hospital inpatient, most services they receive during that stay are paid as a single package to the hospital. M2 tells you the payer matched your service date to an inpatient admission and decided your line falls inside that package. It is usually paired with CARC 97, which says the benefit is included in another payment.

Professional services by physicians are generally still billed separately, so M2 most often hits outside suppliers, labs, imaging centers, DME suppliers, or ambulance companies that billed the payer directly for something furnished during the stay. It is a Medicare-rooted remark but other payers use it as well.

Common causes

A lab, imaging center, or supplier billed directly for a service delivered while the patient was admitted.
The patient’s admission and discharge dates overlap the date of service and the billing office did not know about the stay.
The admission was backdated or converted from observation to inpatient after the fact.
A date of service was entered incorrectly and falls inside an unrelated stay.

What to do

Confirm the patient’s inpatient dates with the hospital. Check whether the service date truly falls inside the stay.
If the date was wrong, submit a corrected claim with resubmission code 7 and the right date in box 24A.
If the service was during the stay, bill the hospital under your arrangement instead of the payer.
If you believe the patient was not an inpatient (for example, they were an outpatient in observation), gather the facility records and request reconsideration.

How to prevent it

Ask referring facilities for admission status before billing, and build a check for recent hospital stays when eligibility responses show them. Checking claims before submission with the Claims Validator can catch date conflicts early. For more on how bundling works in general, see NCCI bundling denials.

Codes that may appear with M2

CO-97 (The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated.): The benefit for this service is included in the payment for another service, here the inpatient stay.
CO-109 (Claim/service not covered by this payer/contractor.): Sometimes used when the claim should have gone to the facility or another payer entity instead of being billed separately.
CO-236 (This procedure or procedure/modifier combination is not compatible with another procedure or procedure/modifier combination provided on the same day…): Can appear when the service is not compatible with the patient's inpatient status on that date.

M97 (Not paid to practitioner when provided to patient in this place of service.): Payment is included in the facility's reimbursement because of the place of service, not specifically an inpatient stay.
MA133 (Claim overlaps inpatient stay.): The claim overlaps an inpatient stay and only services outside the stay should be rebilled.
M96 (The technical component of a service furnished to an inpatient may only be billed by that inpatient facility.): Specific to the technical component of a service furnished to an inpatient, which only the facility may bill.
M15 (Separately billed services/tests have been bundled as they are considered components of the same procedure.): Bundling between services on the same claim, rather than bundling into an inpatient stay.

M2 FAQ

Which services commonly get M2?

Services that are supposed to be furnished under arrangement with the hospital during an inpatient stay, such as certain diagnostic tests, supplies, or ambulance and outpatient services billed by an outside entity.

Can the outside supplier get paid?

Usually by the hospital, under an arrangement, rather than by the payer. The hospital's inpatient payment is meant to cover these services.

Can I bill the patient for an M2 line?

No, when it comes with the CO group code. The service is covered by the inpatient payment, so the patient is not liable for it separately.

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