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Glossary - A


This glossary explains terms in the Medicare program.



A process where external organizations (or "accrediting bodies") evaluate health care facilities' policies, procedures, and performance to make sure they are meeting predetermined criteria.

Advance Beneficiary Notice of Noncoverage (ABN)

In Original Medicare, a notice that a doctor, supplier, or provider gives a person with Medicare before furnishing an item or service if the doctor, supplier, or provider believes that Medicare may deny payment. In this situation, if you aren't given an ABN before you get the item or service, and Medicare denies payment, then you may not have to pay for it. If you are given an ABN, and you sign it, you'll probably have to pay for the item or service if Medicare denies payment.

Advance coverage decision

A notice you get from a Medicare Advantage Plan letting you know in advance whether it will cover a particular service.

Advance directive

A written document stating how you want medical decisions to be made if you lose the ability to make them for yourself. It may include a living will and a durable power of attorney for health care.


Amyotrophic lateral sclerosis, also known as Lou Gehrig's disease.

Ambulatory surgical center

A facility where certain surgeries may be performed for patients who aren’t expected to need more than 24 hours of care.

Angina pectoris

Chest pain.


A medical procedure used to open a blocked artery.


An appeal is the action you can take if you disagree with a coverage or payment decision made by Medicare, your Medicare health plan, or your Medicare Prescription Drug Plan. You can appeal if Medicare or your plan denies one of these:

  • Your request for a health care service, supply, item, or prescription drug that you think you should be able to get
  • Your request for payment for a health care service, supply, item, or prescription drug you already got
  • Your request to change the amount you must pay for a health care service, supply, item or prescription drug.

You can also appeal if Medicare or your plan stops providing or paying for all or part of a service, supply, item, or prescription drug you think you still need.


An agreement by your doctor, provider, or supplier to be paid directly by Medicare, to accept the payment amount Medicare approves for the service, and not to bill you for any more than the Medicare deductible and coinsurance.

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This glossary explains terms in the Medicare program, but it isn't a legal document. The official Medicare program provisions are found in the relevant laws, regulations, and rulings.