Medicare Part B covers preventative services when patients visit approved health care providers, as well as medically necessary treatments and services. Each state has companies that process Medicare claims to determine whether a particular treatment is medically necessary and eligible for coverage, according to Medicare.gov.
Covered services often include ambulance transport, medical equipment and second opinions prior to surgery. Even when Part B covers a procedure or treatment, patients still must pay their $147 yearly deductible and 20 percent of the Medicare-approved cost of each service, Medicare.gov notes. Most Part B beneficiaries also pay a monthly premium of $104.90 as of 2015, although high-income earners may pay more.