Prevention is getting a bad rap--a growing number of health economists and providers are casting doubt on the ability of preventive medicine to squeeze costs out of the health care system. Meanwhile, every state that's proposed health care reform--and now the national effort, as well--carries the promise that part of the costs of the new program will be covered by savings from preventive measures.

Here's Dr. Abraham Verghese expressing his doubts--not about the need to practice prevention, but about the savings that would flow from it. The professor at Stanford University's medical school points out that when doctors screen non-symptomatic patients for high cholesterol, all they are discovering is "a risk factor and not a disease." For those with a high count, the doctor is likely to prescribe a statin drug, which can help prevent heart attacks. "You may have to treat several hundred people to prevent one heart attack," he says. Using a statin costs about $150,000 for every year of life it saves in men. His bottom line: "I don't see the savings there."

The statin argument is making the health-reform rounds--Verghese isn't the only one articulating it--but there is something missing in the discussion: a common definition about what we mean when we talk about preventive care. That's where Judy Monroe's Power Point slides come in handy. Monroe, a physician who's currently the top state health official in Indiana, parses discussions about prevention into three tiers: primary, secondary and tertiary. "There is an order of prevention," she says.

Primary prevention is the place where the costs are low but the potential for savings is large. Mostly, it is the domain of public health and aimed at the general population. This category of prevention includes things like immunization shots, nutrition counseling and prenatal care to avoid neural-tube defects in newborns. "Primary prevention," Monroe says, "means it never occurs."

Secondary prevention, which is largely the domain of primary care physicians, is aimed at individuals . It means detecting and preventing the progression of conditions before they turn symptomatic--for example, screening for high blood pressure and treating it before it turns into a disease. There's a higher cost here, and savings, as Verghese notes, are not likely.

Tertiary prevention is expensive. It's where the medical community tries to prevent the progression of a disease that already is occurring. The idea of investing in primary preventive medicine is to cut back on the need for tertiary measures.

But are there real savings in primary prevention? Researchers at Harvard Medical School studied the return on investment from mobile health clinics--vans that roll out into underserved neighborhoods and bring preventive medicine to people who have little access to care. In particular, Harvard looked at a program called Family Van, a clinic on wheels. Its staff can provide immunization shots, screen for obesity, depression, diabetes, vision and hypertension--and counsel patients on diet and the importance of physical activity. It's typical of what the 2,000 mobile health clinics operating throughout the country do in terms of prevention.

Researchers took Family Van's data for services provided in 2008 and plugged them into an algorithm they had developed to quantify the value of an investment in mobile health care to the overall health care system. The ROI they came up with was a $36 return for every $1 invested.