Patrick Fontana twisted his left knee last spring while hitting a drive down the fairway on a golf course in Columbus, Ohio. But what really pained him was the $900 bill for diagnostic imaging ordered by his doctor.

Mr. Fontana, a 42-year-old salesman, has a high-deductible health plan coupled to a health savings account. Since he was nowhere near meeting his deductible, he was on the hook for the entire bill.

So he did something that insurance companies routinely do: he forwarded the bill to a claims adjuster, in this case My Medical Control, a Web-based company that reviews doctor and hospital bills for consumers.

After concluding that Mr. Fontana was not getting the best possible price, the company’s representatives called the imaging facility and demanded a lower one, promptly saving him $200 — minus a 35 percent collection fee.