According to a report from the Medicare Payment Advisory Commission (Medpac), Medicare is the largest single purchaser of health care in the United States. Of the $2.7 trillion spent on personal health care in 2015, Medicare accounted for 22% or $605 billion. The amount includes spending on direct patient care and excludes certain administrative and business costs.
The report can be obtained at http://medpac.gov/docs/default-source/data-book/jun17_databookentirereport_sec.pdf?sfvrsn=0.