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M28 Remark Code: Not Payable Under Part B Alone

M28 means Medicare Part B will not pay this service even though the patient's Part A coverage was exhausted or not available. Only certain services qualify for Part B payment in that situation, and this was not one of them.

Quick facts

Code
M28 (RARC M28)
Status
Active In use since January 1, 1997.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The facility absorbs the amount unless a proper notice made the patient liable.
  • PR (Patient Responsibility): The patient may be responsible where they were notified in advance that Medicare would not pay.
Official description
This does not qualify for payment under Part B when Part A coverage is exhausted or not otherwise available.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What M28 means

Medicare Part A covers inpatient hospital and skilled nursing facility stays for a limited number of days per benefit period. When those days run out, or when the patient never had Part A for the stay, the facility can still bill Part B for a limited set of medical and other health services. M28 says the service you billed is not on that list, so Part B will not pay either.

This remark applies only to Medicare, and is mostly seen on institutional claims from hospitals and SNFs.

Common causes

  • Room, board, or routine services were billed to Part B after Part A exhaustion.
  • A service that Part B covers only as an outpatient benefit was billed under the Part B inpatient bill type.
  • The facility assumed all ancillary services qualify for Part B.
  • Part A entitlement was not verified before the stay.

What to do

  1. Confirm the patient’s Part A status and benefit days for the stay.
  2. Check whether the service qualifies for Part B payment when Part A is unavailable.
  3. Correct the claim if the service qualifies and was billed under the wrong bill type or revenue code.
  4. Bill any secondary coverage with the Medicare remittance attached.
  5. Bill the patient only if a proper advance notice was given.

How to prevent it

Track benefit day counts for long stays and check entitlement at admission. For the eligibility side, see eligibility and COB denials.

Codes that may appear with M28

  • CO-96 (Non-covered charge(s).): The service is non-covered under Part B in this situation.
  • CO-109 (Claim/service not covered by this payer/contractor.): The service is not covered under this benefit and belongs to another program or payer.
  • N374 (Primary Medicare Part A insurance has been exhausted and a Part B Remittance Advice is required.): Part A is exhausted and a Part B remittance advice is required, which comes up when billing secondary coverage.
  • N121 (Medicare Part B does not pay for items or services provided by this type of practitioner for beneficiaries in a Medicare Part A covered Skilled…): Part B does not pay certain practitioner services for patients in a Part A covered SNF stay.
  • PR-119 (Benefit maximum for this time period or occurrence has been reached.): The benefit maximum for the period has been reached.

M28 FAQ

When can Part B pay for inpatient services?

When a patient has no Part A coverage for a stay, or has exhausted it, hospitals and SNFs can bill Part B for a defined list of ancillary services. Room, board, and routine nursing are not included.

Which claim type is used for Part B inpatient services?

Institutional providers use specific Part B inpatient bill types. Check Medicare's claims processing instructions for the bill type that fits the facility.

What should I do if the patient has other coverage?

Bill the secondary or supplemental payer with the Medicare remittance showing the exhaustion or denial.