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Test ID: TT    
Thrombin Time (Bovine), Plasma

Useful For Suggests clinical disorders or settings where the test may be helpful

The main utility of the thrombin time test is to detect or exclude the presence of heparin or heparin-like anticoagulants (which act by enhancing antithrombin's inhibition of thrombin and other procoagulant enzymes) when used in conjunction with the reptilase time (RT) in evaluating unexplained prolonged clotting times.

 

Identifying the cause of a prolonged prothrombin time, activated partial thromboplastin time, or dilute Russell's viper venom time when used in conjunction with the RT and fibrinogen assay

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Prolonged clotting times may be associated with a wide variety of coagulation abnormalities including:

-Deficiency or functional abnormality (congenital or acquired) of many of the coagulation proteins

-Deficiency or functional abnormality of platelets

-Specific factor inhibitors

-Acute disseminated intravascular coagulation

-Exogenous anticoagulants (eg, heparin, warfarin)

 

The prothrombin time and activated partial thromboplastin time are first-order tests for coagulation abnormalities and are prolonged in many disorders. A battery of coagulation tests is often required to determine the cause of prolonged clotting times.

 

Thrombin catalzyes the transformation of fibrinogen to fibrin (by cleaving fibrinpeptides A and B), which is followed by polymerization of fibrin to form a clot.  The thrombin time (TT) test measures the time of clot formation when thrombin is added to citrated plasma. The phospholipid-dependent procoagulant enzyme cascades (intrinsic, extrinsic, and "common" pathway) are bypassed by the addition of exogenous thrombin. Therefore, the TT mainly reflects functions and interactions of solution-phase exogenous thrombin and endogenous fibrinogen.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

15-23 seconds

Interpretation Provides information to assist in interpretation of the test results

Prolongation of the thrombin time (TT) is consistent with the presence of heparin-like anticoagulants, hypofibrinogenemia, dysfibrinogenemia, fibrin degradation products, and antibody inhibitors of thrombin. An immeasurably prolonged TT is usually the result of heparin in the specimen or, rarely, the presence of thrombin antibodies or afibrinogenemia.

 

When the TT test is performed with diluted bovine thrombin to achieve a normal plasma clotting time of about 20 seconds, the TT is capable of detecting unfractionated heparin at a concentration of 0.05 units/mL of heparin.

 

Other tests useful in interpreting the significance of prolongation of the TT include: reptilase time (RT), human thrombin time, clottable fibrinogen assay, and the fibrin D-dimer assay. These tests are available as components of coagulation profile test panels. As seen in the following table, RT can help distinguish among the various causes of a prolonged TT.

 

Thrombin Time

Reptilase Time


Causes


Remarks

Prolonged

Prolonged

Hypo- or afibrinogenemia

Ascertain by determination of fibrinogen

Prolonged

Prolonged

Dysfibrinogenemia

Ascertain by specific assay

Prolonged

Normal

Heparin or inhibitor of thrombin

Differentiate by human TT and/or heparin assays

Prolonged

Prolonged

Fibrin(ogen) split products (FSP)

Ascertain by FSP or D-dimer assay

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

The thrombin time test, by itself, has little diagnostic value and should be interpreted within the context of additional coagulation assays (eg, prothrombin time, activated partial thromboplastin time, and reptilase time).

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. Koepke JA: Coagulation testing systems. In Practical Laboratory Hematology. New York, Churchill Livingston, 1991

2. Corriveau DM, Fritsma G: Hemostasis and Thrombosis in the Clinical Laboratory. Philadelphia, JB Lippincott Company, 1988

3. Galanakis DK: Plasma thrombin time and related tests. In Williams Hematology. Fifth edition. New York, McGraw-Hill Book Company, 1995, pp L91-L93

4. Greaves M, Preston FE: Approach to the bleeding patient. In Hemostasis and Thrombosis: Basic Principles and Clinical Practice. Fourth edition. Edited by RW Colman, J Hirsh, VJ Marder, et al. Philadelphia, JB Lippincott Company, 2001, pp 783-837

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test