Casting the screening net: separating big fish from little fish

Screening tests are a rapidly growing part of medical practice. If we are going to make the best use of resources, screening tests need to be considered in terms of effectiveness, efficiency and equity. We present a framework as a way to think about screening programmes. The framework expands on existing literature that recognizes two categories of screening: universal and opportunistic. By adding the dimension of 'selectivity', we identify four categories of screening: active non-selective (universal or mass screening), active selective, opportunistic non-selective and opportunistic selective. We illustrate the framework by categorizing screening recommendations for high serum cholesterol levels. We conclude there is no one ideal strategy for screening that simultaneously satisfies criteria of effectiveness, efficiency and equity. However, our framework allows a systematic consideration and balancing of these objectives in the development and assessment of screening programs. In this way, it may assist decision-makers by making this trade-off more explicit.