The thrombin time (TT), also known as the thrombin clotting time (TCT), is a

blood test A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a hypodermic needle, or via fingerprick. Multiple tests for specific blood components, such as a glucose test or a ch ...

that measures the time it takes for a

clot A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of c ...

to form in the plasma of a blood sample containing

anticoagulant Anticoagulants, commonly known as blood thinners, are chemical substances that prevent or reduce coagulation of blood, prolonging the clotting time. Some of them occur naturally in blood-eating animals such as leeches and mosquitoes, where t ...

, after an excess of

thrombin Thrombin (, ''fibrinogenase'', ''thrombase'', ''thrombofort'', ''topical'', ''thrombin-C'', ''tropostasin'', ''activated blood-coagulation factor II'', ''blood-coagulation factor IIa'', ''factor IIa'', ''E thrombin'', ''beta-thrombin'', ''gamma- ...

has been added. It is used to diagnose blood

coagulation Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanis ...

disorders and to assess the effectiveness of fibrinolytic therapy. This test is repeated with pooled plasma from normal patients. The difference in time between the test and the 'normal' indicates an abnormality in the conversion of

fibrinogen Fibrinogen (factor I) is a glycoprotein complex, produced in the liver, that circulates in the blood of all vertebrates. During tissue and vascular injury, it is converted enzymatically by thrombin to fibrin and then to a fibrin-based blood ...

(a soluble protein) to fibrin, an insoluble protein. The thrombin time compares the rate of clot formation to that of a sample of normal pooled plasma. Thrombin is added to the samples of plasma. If the time it takes for the plasma to clot is prolonged, a quantitative (fibrinogen deficiency) or qualitative (dysfunctional fibrinogen) defect is present. In blood samples containing

heparin Heparin, also known as unfractionated heparin (UFH), is a medication and naturally occurring glycosaminoglycan. Since heparins depend on the activity of antithrombin, they are considered anticoagulants. Specifically it is also used in the trea ...

, a substance derived from snake venom called

batroxobin Batroxobin, also known as reptilase, is a snake venom enzyme with Venombin A activity produced by '' Bothrops atrox'' and '' Bothrops moojeni'', venomous species of pit viper found east of the Andes in South America. It is a hemotoxin which act ...

(formerly reptilase) is used instead of thrombin. Batroxobin has a similar action to thrombin but unlike thrombin it is not inhibited by heparin. Normal values for thrombin time are 12 to 14 seconds. If batroxobin is used, the time should be between 15 and 20 seconds. Thrombin time can be prolonged by heparin, fibrin degradation products, and fibrinogen deficiency or abnormality.

Test procedure

After separating the plasma from the whole blood by

centrifugation Centrifugation is a mechanical process which involves the use of the centrifugal force to separate particles from a solution according to their size, shape, density, medium viscosity and rotor speed. The denser components of the mixture migrate ...

, bovine

is added to the sample of plasma. Clot formation is detected optically or mechanically by a coagulation instrument. The time between the addition of the thrombin and the clot formation is recorded as the thrombin clotting time.

Specimen requirements

Whole blood is taken with either

citrate Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in t ...

oxalate Oxalate (IUPAC: ethanedioate) is an anion with the formula C2O42−. This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (Na2C2O4), and several esters such as dimethyl ...

additive (if using the

vacutainer A vacutainer blood collection tube is a sterile glass or plastic test tube with a colored rubber stopper creating a vacuum seal inside of the tube, facilitating the drawing of a predetermined volume of liquid. Vacutainer tubes may contain addi ...

system, this is a light blue top tube). As with other coagulation assays, the tube must not be over- or under-filled in order to ensure the correct anticoagulant-to-blood ratio: one part anticoagulant per nine parts blood.

Reference ranges

The reference ranges of the thrombin clotting time is generally <22 seconds, and from 14 to 16 seconds. Laboratories usually calculate their own ranges, based on the method used and the results obtained from healthy individuals from the local population. Separate ranges are used for infants.

Limitations

Blood samples that are more than eight hours old can give inaccurate results when tested.

References

External links