reptilase

Reptilase refers to a proteolytic enzyme derived from snake venom, used in clinical coagulation testing. The reptilase time (RT) is a laboratory assay that uses this venom to convert fibrinogen to fibrin, producing clot without initiating the full cascade of coagulation. The reagent acts on fibrinogen to release fibrinopeptides and form a fibrin clot, but it does not activate coagulation factors such as thrombin and does not rely on Factor XIII for clot stabilization.

RT is primarily used to assess fibrinogen status and function, and to distinguish abnormalities of fibrinogen from anticoagulants or other coagulation factor deficiencies. Because the reptilase enzyme is not inhibited by heparin, RT is generally insensitive to heparin contamination, in contrast to the thrombin time (TT), which is prolonged by heparin. A prolonged RT usually indicates quantitative reduction of fibrinogen (hypofibrinogenemia) or qualitative fibrinogen disorders (dysfibrinogenemia). A normal RT with a prolonged TT can help point toward the presence of heparin in the specimen. Conversely, a prolonged RT in the setting of a normal thrombin time may suggest a dysfibrinogenemia or other fibrinogen dysfunction, whereas factor XIII deficiency does not typically prolong RT.

Reptilase testing is one component of a broader coagulation workup and is often used when there is suspicion of fibrinogen abnormality or to differentiate between heparin effect and true fibrinogen deficiency. Limitations include inter-laboratory variability and the influence of very abnormal fibrinogen levels on interpretation. See also thrombin time and fibrinogen assays.