Reference Range
Thrombin time is a screening coagulation test designed to assess fibrin formation from fibrinogen in plasma.
The reference range for the thrombin time is usually less than 20 seconds (ie, 15-19 seconds), but this depends on the test kit/instrumentation used in the laboratory. Healthy infants up to age 6 months may have a slightly prolonged thrombin time by 2-3 seconds.
Interpretation
A normal thrombin time excludes abnormalities in the fibrin formation process of the coagulation cascade.
A shortened thrombin time is rare and is observed in patients treated with dextran or hydroxyethyl starch or in individuals with certain forms of hereditary dysfibrinogenemia. [1]
A prolonged thrombin time indicates a fibrinogen abnormality, impairment of fibrin formation, and/or a thrombin inhibitory effect.
Fibrinogen abnormalities include the following:
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Severe hypofibrinogenemia (fibrinogen level < 0.7-1 g/L) or afibrinogenemia (congenital or acquired)
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Congenital or acquired dysfibrinogenemia [1]
Impairments of fibrin formation include the following:
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Disseminated intravascular coagulation (presence of fibrin degradation products, D-dimer)
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Abnormal circulating proteins due to amyloidosis or multiple myeloma
Thrombin inhibitory effects include the following:
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Heparin, hirudin, and direct thrombin inhibitors
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Circulating antibodies to thrombin
Collection and Panels
Specimen: Citrated plasma
Collection: Blue-top tube with 3.2% sodium citrate
Centrifugation: 2000-2500 g for 15 minutes or similar regimen to produce platelet-poor plasma
Storage: Up to 8 hours at room temperature (samples with heparin up to 2 hours); plasma sample should be frozen within 1-2 hours; specimen is stable for one month at -20°C, or 6-9 months at -80°C
Background
Description
Thrombin time is a screening coagulation test designed to assess fibrin formation from fibrinogen in plasma. Thrombin time is performed as the next step in the evaluation of abnormally prolonged activated partial thromboplastin time (aPTT) or prothrombin time (PT). [4]
Indications/Applications
The thrombin time is used to assess unexplained prolongation of PT or PTT (often with conjunction with reptilase time).
Considerations
The thrombin time is very sensitive to unfractionated heparin (≥0.05 U/mL) and might be used for detection of accidental heparin contamination of a plasma specimen.
Low albumin levels (< 30 g/L) in the plasma sample can cause thrombin time prolongation due to delayed fibrin polymerization. [5]
A study by Fliervoet et al indicated that thrombin time results using capillary blood samples are comparable to those using venous blood samples; the same held true for the capillary/venous results for the international normalized ratio (INR), PT, fibrinogen, and D-dimer. The investigators determined the mean relative difference in thrombin time between capillary and venous samples to be -1.7%. [6]
