Each year, millions of patients visit their doctors’ offices for a variety of routine services. But in recent years, more Americans are being charged as if they had visited a hospital. And it is because the doctor’s office billing them is, in fact, pretending to be a hospital.

When a hospital bills a patient’s insurer, it must report a federally required National Provider Identifier number on the claim form to identify where the care took place. Many hospitals use the same NPI number for care that happens at a doctor’s office or the main hospital, allowing hospitals to add a facility fee and charge far more than they would for a doctor’s visit.