Medical tests like MRIs, CT scans, and X-rays can be helpful. But the problem with them – and the reason a task force recently recommended that doctors limit the number of tests they order – is that medical screening often finds abnormalities that aren't the root of a patient's problem.

In the case of many complaints, such as lower-back pain, medical tests offer little insight, and the prescription remains the same: rest. If a doctor orders you an X-ray, then a CT, and then an ultrasound, all in his own lab, you should run the other way, says Mordkin, because it's likely that physician stands to profit from the tests, and you can't be sure whether he's operating with his or your best interests in mind. On the other hand, "If we're concerned you have something serious, like a kidney stone, and you're in a lot of pain, that's a good time to get a CT scan of your kidney. It depends on your symptoms and presentation."

Bottom line: Ask your doctor why you need that test, what he hopes to tell from the results, and how it will affect your treatment.