Thrombin time
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The Thrombin Time (TT), is a blood test which measures the time it takes for a clot to form in the plasma from a blood sample in anticoagulant which had added an excess of thrombin,[1]. 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.[2] 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 fibrinogen deficiency 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, lupus anticoagulant.
Procedure
Within the realm of coagulation 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
Specimen Requirements
Whole blood is taken with either citrate 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.
Reference Interval
The reference interval of the Thrombin Clotting time is generally <22 seconds,[3] depending on the method and the endemic patient population. Results outside of reference interval indicate heparin therapy, Hypofibrinogenemia, hyperfibrinogenemia fibrinogen abnormality, or Lupus anticoagulant.
Causes for specimen rejection
Causes for Rejection of the specimen include QNS, severe hemolysis, improper storage or delay in processing, error in labeling.
References
- ^ "thrombin time" at Dorland's Medical Dictionary
- ^ Flanders MM, Crist R, Rodgers GM (2003). "Comparison of five thrombin time reagents". Clin. Chem. 49 (1): 169–72. PMID 12507975.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: multiple names: authors list (link) - ^ Gastineau DA, Gertz MA, Daniels TM, Kyle RA, Bowie EJ (1991). "Inhibitor of the thrombin time in systemic amyloidosis: a common coagulation abnormality". Blood. 77 (12): 2637–40. PMID 1904284.
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