Factor V Leiden.

Factor V Leiden (FVLeiden ) is a common hereditary thrombophilia that causes activated protein C (APC) resistance. This review describes many of the most fascinating features of FVLeiden , including background features, mechanisms of hypercoagulability, the founder mutation concept, the "FVLeiden paradox," synergistic interaction with other thrombotic risk factors, the intertwined relationship between FVLeiden and APC resistance testing, and other, uncommon mutations implicated in causing APC resistance. In addition, there are several conditions where laboratory tests for APC resistance and FVLeiden are or can be discrepant, including lupus anticoagulants, anticoagulants such as direct thrombin inhibitors (dabigatran, argatroban, and bivalirudin) and rivaroxaban, as well as pseudohomozygous, pseudo-wildtype, liver transplant, and bone marrow transplant patients. The laboratory test error rate for FVLeiden is also presented.