[Hunger for testing satisfied].

Our view on causes of venous thrombosis changed drastically by the discovery of Factor V Leiden, since unlike other genetic causes of hereditary thrombophilia its prevalence is several percent. It led to major research activities, and the insight that thrombosis is a multicausal disease, invariably the result of an interplay of genetic and environmental factors. Another consequence was a hype of testing of thrombosis patients, and women before starting oral contraceptives. Factor V Leiden became the most performed diagnisticgenetic test worldwide. However, there was no medical rationale for this massive testing. In young women the absolute risk of thrombosis is so low, that enormous numbers of women would need to be tested to prevent one thrombotic event. And tests after a first event in patients were nearly always useless, since Factor V Leiden does not affect the risk of recurrence. It took decennia before the hype faded.