The thrombin time (TT) may sometimes be used as part of an investigation of a possible bleeding disorder or inappropriate blood clot formation (thrombotic episode), particularly to evaluate the level and function of fibrinogen.
The clotting-based functional fibrinogen assay is now routinely available in clinical laboratories and has largely replaced the need for thrombin time for evaluation of fibrinogen.
This test is very sensitive to the anticoagulantheparin. Because of this, it was once used to monitor unfractionated heparin therapy and to detect heparin contamination in a blood sample. While it is still sometimes used for these purposes, other tests and heparin neutralization procedures have largely replaced it.
A thrombin time may be ordered by itself or along with a combination of other tests when a person has bleeding or clotting episodes, experiences recurrent miscarriages, or has unexplained prolonged results on primary coagulation tests such as prothrombin time (PT) or partial thromboplastin time (PTT).
This test may be ordered when a health practitioner suspects that a person may have a disorder associated with decreased or dysfunctional fibrinogen. However, as mentioned previously, the functional fibrinogen assay (with or without a fibrinogen antigen assay) has largely replaced thrombin time for evaluating fibrinogen.
A thrombin time may sometimes be ordered when heparin contamination of a sample is suspected or when a person is receiving heparin therapy, although these uses have declined.
Significantly prolonged thrombin times are most commonly found when there is contamination of the blood sample by the anticoagulantheparin, direct thrombin inhibitor, and may be seen with heparin-like substances and inhibitors (e.g., fibrinogen/fibrin degradation products). Contamination can occur when a person is on heparin therapy and/or when heparin is used as a periodic flushing agent to keep intravenouscatheters from clotting.
The thrombin time is just one component of the battery of tests typically required to evaluate a bleeding or thrombotic disorder.
A significant percentage of people with decreased or dysfunctional fibrinogen will have no symptoms or mild symptoms and may only be diagnosed if the abnormality is discovered during testing for another reason, or because they have unexpected or prolonged bleeding following a surgical procedure or trauma.
Fibrinogen is one of several blood factors that are called acute phase reactants. Blood levels of fibrinogen along with other acute phase reactants rise sharply with conditions causing acute tissue inflammation or damage.
Genetic molecular testing is occasionally performed on those with inherited dysfibrinogenemia, hypofibrinogenemia, or afibrinogenemia to identify the genetic mutation responsible. Testing for this mutation may also be performed on other family members.
Some recurrent miscarriages are thought to be related to inappropriate clotting in placental blood vessels.
This article was last reviewed on May 2, 2014. | This article was last modified on May 2, 2014.
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