What the notice tells you
The MSN lists Part A or Part B services and supplies billed to Medicare during the period, what Medicare paid, whether a claim was approved, and the maximum amount you may owe the provider or supplier. It also gives instructions for questions, suspected errors, and appeals.
What to do before paying
Compare the MSN with the actual provider bill, receipts, and statements from Medigap or other insurance. Confirm that you received every listed service and that the dates match. The amount marked as the maximum you may be billed does not account for every payment another insurer may make and is not itself a payment request.
If the information looks wrong
Contact the provider or supplier about an incorrect service, date, or submission. If Medicare denied an item because the claim information was wrong, the provider may be able to correct and resubmit it. If you disagree with Medicare's decision, use the appeal date and instructions on the last page of that MSN.
When this answer changes
Medicare Advantage and Medicare drug plans generally send an Explanation of Benefits rather than an Original Medicare MSN. That document is also a summary, but the plan controls the claim details, billing questions, and appeal instructions.