Medical bills are not designed to make sense to the patient. In fact, as I’ve written before, they are almost impossible to understand, even when the charges are explained by the billing office.
So it’s pretty easy for hospitals to add charges to the bill without the patient really knowing. One popular way is to add a “facility fee”.
My daughter in on a medication that is given once every 2 months. She goes to the doctors’ office building that is connected to an academic medical center where the medication is given through an IV over the course of a few hours. The staff members in the infusion center know her well and her doctor often stops by to say hello while she is there.