These new fees are worrisome to health advocates. At a time when the country is trying to hold down health care costs, payments from patients shift spending to a place where they cannot be readily tallied. Also, such fees often undercut mandates under the Affordable Care Act that certain vital services for women’s health and preventive care be provided at no cost to patients: An intrauterine device is covered, but there is an insertion fee. An annual physical is covered, but not some of the blood work that a physician has ordered.

Knowing that his new policy under the Affordable Care Act covered preventive care, Kyle Thompson-Westra, 28, a business student in Chicago, selected a doctor in his network and went in January to get his first physical in years.

His insurer paid the doctor’s office about $600 of the $900 bill. He owed over $300 for blood work. There were several tests, such as thyroid function, that the doctor considered part of a routine physical, but that the insurer insisted were not.

The Affordable Care Act gives guidance on what kinds of exams must be covered at no cost as preventive services. But Clare Krusing, a spokeswoman for America’s Health Insurance Plans, an industry group, said, “If a provider chooses to do something beyond what’s covered, there may be charges.”

Medicare requires doctors to inform its patients in advance about any service they are dispensing that they believe the government insurer will not cover, and provide an accurate estimate of what the patient will have to pay. But there are no such protections in commercial insurance.