President Obama has a prescription for those receiving unnecessary tests and treatments: focus on what's important and add an ounce of prevention.

"Things like mammograms and cancer screenings and immunizations -- common-sense measures that will save us billions of dollars in future medical costs," he said at a town hall meeting hosted by AARP last month.

It seems reasonable enough that "unnecessary" tests can add up, and "necessary" tests like cancer screenings might catch disease early enough to prevent expensive medical procedures and prescription drugs down the line.

Or maybe not.

"When you talk about prevention that involves visiting a doctor and stumbling upon a high cholesterol that you didn't know about or a high blood pressure, that kind of medical prevention almost inevitably leads to more medical things being done, more medications being prescribed," Dr. Abraham Verghese of the Stanford University School of Medicine told FOX News.

After more tests, a patient with high cholesterol could be prescribed a statin, which might reduce his chance of a heart attack. But because only one or two men among several thousand with high cholesterol might suffer a heart attack, that ounce of prevention could be too costly.

"If you're looking at a population of men, for every life you save, it costs $150,000 to extend life by one year, in terms of statin use," Verghese said.

And take prostate cancer. The current Prostate Specific Antigen or PSA screenings are sensitive enough to detect cancers that may never even impair patients. But doctors can't yet predict which are harmless and which are deadly, meaning that radiation or surgery could leave some of those with harmless cancers feeling worse than if they'd been never been treated.

There is one ounce of prevention that everyone agrees would help cut cuts: exercise, lose weight, watch your diet, cut down on cigarettes and alcohol. But that's easier said than done. Some lawmakers working on the health care legislation believe that the only way to accomplish those behavioral changes is to reward them.

"If there is a real incentive, what happens once you get people into it," said Sen. Tom Coburn, R-Okla., who is a physician. "They like it -- 'I am feeling better, I'm active.'"

There are other problems with preventive care. How do you change a patient's attitude that "my test is important but not the one for the guy down the hall?"

And will government-run health care mean rationing of tests? Doctors say without tort reform they'll continue to order often unnecessary tests to avoid malpractice suits. Finally, Dough Elmendorf, director of the Congressional Budget Office, says researchers generally find that the added costs of widespread use of preventive services tend to exceed the savings from averted illness.

Mike Emanuel currently serves as chief congressional correspondent for FOX News Channel (FNC). He joined FNC in 1997 as a Los Angeles-based correspondent.