Investigations such as blood tests and radiography are important tools for the making correct diagnoses. The use of diagnostic resources is growing steadily—in the Netherlands, for example, nationwide expenditure on diagnostic tests is growing at the rate of 7% a year. Unfortunately, health status is not improving similarly, which suggests that investigations are being overused. The ordering of tests seems not to be influenced by the fact that their diagnostic accuracy is often disappointing. Considerations other than strict scientific indications seem to be involved, and we may ask whether new knowledge and research findings are adequately reflected in daily practice.

Several factors may be responsible for the increasing use of investigations, such as the increasing demand for care (due to ageing of the population and increasing numbers of chronically ill people); the fact that they are available, which in itself leads to ordering; and the urge to make use of new technology. Once an abnormal test result is found, doctors may order further investigations, not realising that on average 5% of test results are outside their reference ranges, and a cascade of testing may result. Furthermore, higher standards of care, the guidelines for which often recommend additional testing, and defensive behaviour have led to more investigations. Unfortunately, when guidelines on selective and rational ordering of investigations are introduced, numerous motives for ignoring evidence based recommendations, such as fear of litigation, or procrastination on the part of the doctor, come into play in daily practice and are difficult to influence.

Overuse of investigations—and there is reason to believe that some requests are illogical—leads to overloading of the diagnostic services and overexpenditure: more efficient usage is therefore needed. Interventions focusing on overt examples of inappropriate testing might reduce costs while simultaneously improving quality of care.