Abbreviations: F, Frits Rosendaal; J, John Heit; K, Ken Bauer; APC, activated protein C; APCR, APC resistance; MTHFR, methylene tetrahydrofolate reductase; TAFI, thrombin activatable fibrinolysis inhibitor.

^†For F, no testing is done for a first episode of venous thrombosis unless it is exceptional in some way (e.g., very extensive clot, very young individual, positive family history). Thus, test-ordering practices refer to those exceptional first and recurrent events.

^‡For K, hospital laboratories initially test for factor V Leiden by DNA-based assay.