…is that doctors routinely call for unnecessary medical procedures, particularly expensive imaging like CTs or MRIs. From a commentary in this week’s New England Journal of Medicine:

Between 1993 and 2001, the number of myocardial perfusion scans increased by more than 6% per year, with no justification for their use based on disease rates, health care disparities, or newly published, definitive randomized trials. Since 1992, the number of CT scans obtained has quadrupled. Physicians are referring their patients for so many imaging tests that as many as 2% of cancers may be attributable to radiation exposure during CT scanning.

…Most physicians who order imaging tests experience no consequences for incurring costs for procedures of unproven value. On the contrary, they or their colleagues are paid for their services, and their patients don’t complain because the costs are covered by third parties. Patients are pleased to receive thorough evaluations that involve the best cutting-edge technologies. Physicians can easily defend their practices because their specialty societies argue that the procedures are “appropriate.” The issue of radiation exposure is unlikely to come up because each procedure is considered in isolation, the risks posed by each procedure are low and seemingly unmeasurable, and any radiation-induced cancer won’t appear for years and cannot easily be linked to past imaging procedures.

When skeptics complain about excessive costs for unnecessary imaging procedures, it is easy to dismiss them for advocating restriction (even “rationing”) of services that logical constructs argue should help. In the case of myocardial perfusion imaging — the procedure responsible for more radiation exposure than any other, according to the report by Fazel et al. — proponents have argued that abnormalities detected on such scans are powerful predictors of future clinical events. It is logical, the argument goes, that imaging tests may identify patients for whom aggressive therapies should improve the outcome. But this logic represents only a hypothesis, not a proof. One recent trial of myocardial perfusion imaging in patients with diabetes showed no improvement in the  outcome despite an accurate prediction of events. Prediction does not necessarily lead to prevention.