Thrombin clotting time
Encyclopedia
The Thrombin Time is a blood test which measures the time it takes for a clot to form in the plasma of a blood sample anticoagulant
to which an excess of thrombin has been added,. 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
(a soluble protein) to fibrin an insoluble protein.
This test is also known as the Thrombin Clotting Time (TCT).
Thrombin time compares a patient's rate of clot formation to that of a sample of normal pooled plasma. Thrombin is added to the samples of plasma. If the plasma does not clot immediately, a quantitative (fibrinogen
deficiency) or qualitative (dysfunctional fibrinogen) defect is present. If a patient is receiving heparin
, a substance derived from snake venom called reptilase is used instead of thrombin. Reptilase has a similar action to thrombin but unlike thrombin it is not inhibited by heparin.
The thrombin time is used to diagnose bleeding disorders and to assess the effectiveness of fibrinolytic therapy. Reference values for thrombin time are 10 to 15 seconds or within 5 seconds of the control. If reptilase is used, the reptilase time should be between 15 and 20 seconds. Thrombin time can be prolonged by: heparin, fibrin degradation products, factor XIII deficiency, and fibrinogen deficiency/abnormality.
assays, the Thrombin Clotting Time is one of the most procedurally simple. After liberating the plasma from the whole blood by centrifugation
, bovine Thrombin
is added to the sample of plasma. The clot is formed and 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
or oxalate
additive (if using the vacutainer
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: 1 part anticoagulant per 9 parts blood.
, severe hemolysis
, improper storage or delay in processing, error in labeling.
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...
to which an excess of thrombin has been added,. 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
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...
(a soluble protein) to fibrin an insoluble protein.
This test is also known as the Thrombin Clotting Time (TCT).
Thrombin time compares a patient's rate of clot formation to that of a sample of normal pooled plasma. Thrombin is added to the samples of plasma. If the plasma does not clot immediately, a quantitative (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...
deficiency) or qualitative (dysfunctional fibrinogen) defect is present. If a patient is receiving 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...
, a substance derived from snake venom called reptilase is used instead of thrombin. Reptilase has a similar action to thrombin but unlike thrombin it is not inhibited by heparin.
The thrombin time is used to diagnose bleeding disorders and to assess the effectiveness of fibrinolytic therapy. Reference values for thrombin time are 10 to 15 seconds or within 5 seconds of the control. If reptilase is used, the reptilase time should be between 15 and 20 seconds. Thrombin time can be prolonged by: heparin, fibrin degradation products, factor XIII deficiency, and fibrinogen deficiency/abnormality.
Procedure
Within the realm of coagulationCoagulation
Coagulation is a complex process by which blood forms clots. It is an important part of hemostasis, the cessation of blood loss from a damaged vessel, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel...
assays, the Thrombin Clotting Time is one of the most procedurally simple. After liberating the plasma from the whole blood by centrifugation
Centrifugation
Centrifugation is a process that involves the use of the centrifugal force for the sedimentation of mixtures with a centrifuge, used in industry and in laboratory settings. More-dense components of the mixture migrate away from the axis of the centrifuge, while less-dense components of the mixture...
, bovine 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...
is added to the sample of plasma. The clot is formed and 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 citrateCitrate
A citrate can refer either to the conjugate base of citric acid, , or to the esters of citric acid. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate.-Other citric acid ions:...
or oxalate
Oxalate
Oxalate , is the dianion with formula C2O42− also written 22−. Either name is often used for derivatives, such as disodium oxalate, 2C2O42−, or an ester of oxalic acid Oxalate (IUPAC: ethanedioate), is the dianion with formula C2O42− also written (COO)22−. Either...
additive (if using the vacutainer
Vacutainer
Vacutainer is a brand of test tubes specifically designed for venipuncture, which was developed in 1947 by Joseph Kleiner.In phlebotomy the word “vacutainer” has come to be used as a genericized trademark to describe any vacuum-based blood collection vial, regardless of brand. Becton Dickinson...
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: 1 part anticoagulant per 9 parts blood.
Reference Interval
The reference interval of the Thrombin Clotting time is generally <22 seconds, depending on the method and the endemic patient population. Results outside of reference interval indicate heparin therapy, a qualitative deficiency in fibrinogen, Hypofibrinogenemia, or hyperfibrinogenemia.Causes for specimen rejection
Causes for Rejection of the specimen include QNSQNS
QNS is a clinical laboratory abbreviation for Quantity Not Sufficient. This indicates that either1.) There is not enough specimen for the lab tests ordered to be performed....
, severe hemolysis
Hemolysis
Hemolysis —from the Greek meaning "blood" and meaning a "loosing", "setting free" or "releasing"—is the rupturing of erythrocytes and the release of their contents into surrounding fluid...
, improper storage or delay in processing, error in labeling.
External links
- http://peir.path.uab.edu/coag/article_136.shtml
- http://medinfo.ufl.edu/year2/coag/tt.html
- http://www.rnceus.com/coag/coagtt.html
- http://www.utmb.edu/lsg/labsurvivalguide/hem/thrombin_time.htm