Reptilase time is a blood test used to detect deficiency or abnormalities in fibrinogen

Fibrinogen

Fibrinogen is a soluble plasma glycoprotein, synthesised by the liver, that is converted by thrombin into fibrin during blood coagulation. This is achieved through processes in the coagulation cascade that activate the zymogen prothrombin to the serine protease thrombin, which is responsible for...

, especially in cases of heparin

Heparin

Heparin , also known as unfractionated heparin, a highly sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule...

 contamination.

Reptilase, an enzyme found in the venom of Bothrops snakes

Bothrops

Bothrops is a genus of venomous pitvipers found in Central and South America. The generic name is derived from the Greek words bothros and ops that mean "pit" and "eye" or "face"; an allusion to the heat-sensitive loreal pit organs. Members of this genus are responsible for more human deaths in the...

, has activity similar to thrombin

Thrombin

Thrombin is a "trypsin-like" serine protease protein that in humans is encoded by the F2 gene. Prothrombin is proteolytically cleaved to form thrombin in the first step of the coagulation cascade, which ultimately results in the stemming of blood loss...

. Unlike thrombin, reptilase is resistant to inhibition by antithrombin III. Thus, the reptilase time is not prolonged in blood samples containing heparin, hirudin

Hirudin

Hirudin is a naturally occurring peptide in the salivary glands of medicinal leeches that has a blood anticoagulant property...

, or direct thrombin inhibitor

Direct thrombin inhibitor

Direct thrombin inhibitors are a class of medication that act as anticoagulants by directly inhibiting the enzyme thrombin. Some are in clinical use, while others are undergoing clinical development...

s, whereas the thrombin time will be prolonged in these samples. Reptilase also differs from thrombin by releasing fibrinopeptide A, but not fibrinopeptide B, in its cleavage of fibrin

Fibrin

Fibrin is a fibrous, non-globular protein involved in the clotting of blood. It is a fibrillar protein that is polymerised to form a "mesh" that forms a hemostatic plug or clot over a wound site....

.

Other causes of prolonged reptilase time include the presence of fibrin degradation products, which interfere with fibrin polymerization.