Ecarin clotting time is a laboratory test used to monitor anticoagulation during treatment with hirudin

Hirudin

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

, an anticoagulant

Anticoagulant

An anticoagulant is a substance that prevents coagulation of blood. A group of pharmaceuticals called anticoagulants can be used in vivo as a medication for thrombotic disorders. Some anticoagulants are used in medical equipment, such as test tubes, blood transfusion bags, and renal dialysis...

 medication

Medication

A pharmaceutical drug, also referred to as medicine, medication or medicament, can be loosely defined as any chemical substance intended for use in the medical diagnosis, cure, treatment, or prevention of disease.- Classification :...

 which was originally isolated from leech

Leech

Leeches are segmented worms that belong to the phylum Annelida and comprise the subclass Hirudinea. Like other oligochaetes such as earthworms, leeches share a clitellum and are hermaphrodites. Nevertheless, they differ from other oligochaetes in significant ways...

 saliva. Ecarin, the primary reagent in this assay, is derived from the venom of the saw-scaled viper, Echis carinatus

Echis carinatus

Echis carinatus is a venomous viper species found in parts of the Middle East and Central Asia, and especially the Indian subcontinent. It is the smallest member of the Big Four snakes...

.

In the clinical assay, a known quantity of ecarin

Ecarin

Ecarin is an enzyme that is derived from the venom of the Indian saw-scaled viper, Echis carinatus, It is the primary reagent in the Ecarin clotting time test....

 is added to the plasma of a patient treated with hirudin. Ecarin activates prothrombin through a specific proteolytic cleavage, which produces meizothrombin, a prothrombin-thrombin intermediate which retains the full molecular weight of prothrombin, but possesses a low level of procoagulant enzymatic activity. Crucially, this activity is inhibited by hirudin and other direct thrombin inhibitors, but not by 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...

. The ECT is also unaffected by prior treatment with coumadin

Coumadin

*For the rodenticide class of anticoagulant poisons sometimes loosely referred to as coumadins or coumarins, see 4-hydroxycoumarins.*For the pharmaceutical with the trade name Coumadin, see warfarin....

 or the presence of phospholipid-dependent anticoagulants, such as lupus anticoagulant

Lupus anticoagulant

Lupus anticoagulant is an immunoglobulin that binds to phospholipids and proteins associated with the cell membrane. It is important to note that this disease name is actually a misnomer...

. Thus, the ECT is prolonged in a specific and linear fashion with increasing concentrations of hirudin. An enhancemnt of the ECT is the ecarin chromogenic assay (ECA) in which diluted sample is mixed with an excess of purified prothrombin and the generated meizothrombin is measured with a specific chromogenic substrate. This assay shows no interference from prothrombin or fibrinogen in the sample and is suitable for the measurement of all direct thrombin inhibitors .<3>
Lange U, Nowak G, Bucha E. Ecarin chromogenic assay--a new method for quantitative determination of direct thrombin inhibitors like hirudin. Pathophysiol Haemost Thromb. 2003 Jul-2004 Aug;33(4):184-91.