Just to be sure we’re all on the same page, “screening” means we are looking for a disease that already exists in a person, but has not advanced to the stage where it is causing symptoms. Usually, but not always, this means we are using some kind of machine or instrument to look for the disease. Regardless, all screening tests cost money in some way and all have potentials for both medical benefit and medical harm.
Those three qualities – financial cost, medical benefit, and medical harm – are the pillars for any discussion about screening.
If we remove cost from the equation – let’s say our patient is wealthy and happy to pay for anything – questions of over-screening vs. under-screening simply boil down to the patient’s individual taste for balancing the benefit and harm potentials. Ideally, the physician communicates these potentials to the patient clearly and accurately, then lets the patient decide. Some decisions are easy, some are hard, as shown in Figure 1.
In this idealized, cost-ignoring scenario, over-screening and under-screening really do not exist. Some of us might question a patient’s decision-making, but, ultimately, all of us walk in our own moccasins. In the real world, however, communicating benefits and harms is not easy[1] and most patients do not want to make decisions completely on their own: They want guidance from a physician, who is accustomed to thinking about medical trade-offs and living with medical complications.
People who make policy about screening have a much more complicated chore, because they cannot ignore cost – it is added as a third dimension to Figure 1. And, just as different individual persons have different tastes for weighing benefit and harm, so, too, individual societies (or segments of societies) have different tastes for weighing reasonable costs vs. excessive costs.
So, here again, it’s really not possible, on an absolute scale, to say whether there is too much or too little screening.
Certainly, however, support for improving our preventive health capabilities is universal. PSA screening leaves much to be desired because it cannot distinguish between life-threatening prostatic cancers, and those that will ultimately prove harmless. Mammography would be better if it could more reliably distinguish benign from malignant lesions. Although knowledge of the patient’s genome will someday improve the performance of these tests, better biochemical testing is more likely to move us closer to the Holy Grail.
Finally, it is also worth remembering how much screening has already brought us. Apart from the invention of antibiotics, the greatest public health triumph of the 20th century was the reduction in death and disability from heart disease, which had reached epidemic proportions by the 1950s – a rate three-times its level today[2]. No one innovation is responsible for this near-miracle, but the practice of taking blood pressure at every physician visit and the adoption of widespread cholesterol testing were big contributors. In fact, these screening techniques have been so successful that they have expanded the concept of “disease” to encompass what were once called “risk factors.” Screening is now, and forever will be, a major part of medicine.
[1] The Foundation for Informed Medical Decision-Making has pioneered better ways to communicate the potentials for risk and benefit to patients.
[2] See figure 1 in: Nemetz PN, et al. “Recent trends in the prevalence of coronary disease: a population-based autopsy study of nonnatural deaths.” Archives of Internal Medicine. 2008; 168(3): 264-170. Available online at: http://archinte.jamanetwork.com/article.aspx?articleid=413914