Thrombin Time

The thrombin time 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 anticoagulant heparin. 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 you have bleeding or clotting episodes, experience recurrent miscarriages, or have unexplained prolonged results on primary coagulation tests such as prothrombin time (PT) or partial thromboplastin time (PTT).

This test may be ordered when your health care practitioner suspects that you 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 you are 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 anticoagulant heparin, direct thrombin inhibitor (such as dabigatran), and may be seen with heparin-like substances and inhibitors (e.g., fibrinogen/fibrin degradation products). Contamination can occur when you are on heparin therapy and/or when heparin is used as a periodic flushing agent to keep intravenous catheters from clotting.

A prolonged thrombin time may indicate decreased fibrinogen level and/or abnormal fibrinogen function. Conditions such as disseminated intravascular coagulation (DIC), a serious condition that can cause clotting and bleeding, or abnormal fibrinolysis impair fibrin formation and can also lead to a prolonged thrombin time, as can conditions such as end stage liver disease or malnutrition.

If thrombin time is abnormal, additional tests may be needed, including fibrinogen activity assay (now routinely available in clinical laboratories), fibrinogen antigen assay, and liver function tests.

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 fibrinogen-related disorders 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.

With the exception of a PT test, bleeding disorder tests, including the thrombin time, require specialized equipment and reagents and are typically performed in a laboratory.

Yes. For many people, the clotting process functions relatively normally even when fibrinogen concentrations and/or activity are decreased. Your condition may not be identified unless pre-surgery screening identifies a potential problem or you bleed longer than expected after a surgical procedure or trauma.

Treatment is not needed in most cases, but people with significant bleeding may be given fibrinogen replacements like cryoprecipitate or fresh frozen plasma on a short-term basis to replace fibrinogen. Those who have recurrent inappropriate clotting may require anticoagulation therapy with anticoagulants such as warfarin (Coumadin) or heparin.

If heparin is suspected as the cause of a prolonged thrombin time, heparin assays or reptilase time (RT) can be used to confirm heparin presence. Reptilase time measures the time it takes for a clot to form after reptilase has been added to plasma. Thrombin time may be ordered with a reptilase time to investigate a prolonged clotting time. Since thrombin time, but not reptilase time, is affected by the anticoagulant heparin, prolongation of both thrombin time and reptilase time indicates decreased fibrinogen level and/or abnormal function of fibrinogen. If thrombin time is prolonged but reptilase time is normal, heparin contamination or presence of an interfering substance is likely the cause. The clotting-based functional fibrinogen assay is now routinely available in clinical laboratories and has largely replaced the need for thrombin time and reptilase time for evaluation of fibrinogen.

Dabigatran, a direct thrombin inhibitor, is one of the newly approved oral anticoagulants. Routine therapeutic monitoring is not required; however, monitoring may be needed in certain clinical conditions. Thrombin time or a modified plasma-diluted thrombin time (dTT) has been advocated for monitoring dabigatran therapy, but it has not been widely accepted as the standard practice. Instead, direct measurement of dabigatran level should be used if monitoring is indicated.