The corrupt health care system in the United States starts with corrupt doctors who order unnecessary tests for patients in order to make more money. Most of the time, insurance companies or Medicare/Medicaid will be billed for the procedures and tests. There is no loss to the doctors since someone else is paying for it.
Health care in the US is filled with corruptions, which is why health care costs are eating up roughly 18% of US GDP. The "fee for service" model invites lots of unnecessary procedures. Overbilling Medicaid through coding fraud alone costs tens of billions. Medicare fraud is estimated to be as high as 30% of overall spending.