title: HCFA modifies requirements on physician certification for nonemergency ambulance services.
mesh_terms: D000552:Ambulances / Q000191:economics / Q000592:standards*; D014487:Centers for Medicare and Medicaid Services, U.S.; D002568:Certification; D016208:Databases, Factual; D006801:Humans; D006278:Medicare; D014481:United States