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Thrombin Time

Does this test have other names?

Thrombin clotting time

What is this test?

Blood clotting is an important step in healing from an injury, such as a cut. Forming a blood clot is a complicated process, involving many blood components that must interact in a specific order.

Thrombin time is a measure of how long the blood's plasma, or the liquid portion of the blood, takes to form a clot. This test provides information about how well one particular blood component, called fibrinogen, is working. 

Why do I need this test?

Your health care provider may order this test if your blood does not seem to be clotting properly. Abnormal results of the thrombin time test suggest that you may have low or high levels of fibrinogen, or that your fibrinogen is not working properly.

This can be because of:

  • Inherited conditions that lead to low fibrinogen or fibrinogen disorders

  • Liver diseases such as cirrhosis, hepatitis, and liver cancer

  • Cancers such as renal carcinoma (kidney cancer) or multiple myeloma

  • Certain other health conditions, including lupus and ulcerative colitis

  • Surgery that uses fibrin glue created from cow sources; this may cause the body to develop antibodies against fibrinogen

  • Disseminated intravascular coagulation, a condition in which your body uses more fibrinogen

Certain medications can also lead to a longer thrombin time, including:

  • Heparin

  • Warfarin

  • Hirudin

  • Hirulog

  • Argatroban

Symptoms of fibrinogen problems include:

  • Excessive bleeding or bruising

  • Pregnancy problems, including repeated miscarriages early in pregnancy and abnormal bleeding after delivery 

What other tests might I have along with this test?

Your health care provider may recommend other tests to measure your blood's clotting ability. These include:

  • Reptilase time. Like thrombin time, this test measures the conversion of fibrinogen to fibrin. It shows if an unusually long thrombin time is due to heparin.

  • Prothrombin time. This test provides information about fibrinogen and other components that play a role in clot formation. It's also used to measure the effects of warfarin, a blood-thinning drug.

  • Activated partial thromboplastin time. This test also provides information about numerous factors involved in blood clotting and is used to measure the effects of heparin treatment.  

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider. 

The laboratory technician places thrombin from humans or cows in your plasma sample and records the number of seconds needed for it to form a clot. A normal thrombin time is 11.3 to 18.5 seconds.

A longer thrombin time can indicate low fibrinogen, high fibrinogen, or fibrinogen that's not working properly. It can also be because of medications that affect blood clotting, such as heparin, argatroban, hirudin, or hirulog. 

A longer thrombin time can be caused by proteins in the blood from the medical conditions multiple myeloma or amyloidosis, or from antibodies that developed from earlier exposure to bovine thrombin. 

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm. The sample is placed in a tube containing a chemical that keeps it from clotting.

Does this test pose any risks?

Taking a blood sample with a needle carries small risks that include bleeding, infection, bruising, and a sense of lightheadedness. When the needle pricks your arm, you may feel a slight sting or pain. Afterward the site may be sore.

What might affect my test results?

Some medications that alter blood clotting will affect your test results, including heparin and warfarin.

How do I get ready for this test?

Tell your doctor if you're taking any medications, especially those that affect your blood's ability to clot. Tell your doctor about any vitamins, herbs, or supplements you are taking, too. Also discuss any medical conditions you have and any history of unusual bleeding.