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Immunology & Autoimmune
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Currently under review
Pending specialist review and validation.
Thrombin Time is a blood test that measures how long it takes for thrombin to turn fibrinogen into a stable fibrin clot in your plasma. It focuses on the final step of the clotting process, so it helps assess whether fibrinogen is present and functioning and whether anything in the blood is blocking thrombin or fibrin formation.
This test is often used alongside other clotting tests, such as the prothrombin time and activated partial thromboplastin time, to investigate bleeding, bruising, or the effect of certain anticoagulant medicines. It can also help separate problems with fibrinogen from issues earlier in the clotting pathway.
Thrombin Time helps your care team determine why clotting might be delayed. A prolonged result can occur with low or abnormal fibrinogen, with substances that interfere with thrombin or fibrin formation, or with certain anticoagulant medicines that directly inhibit thrombin. It can also be affected in liver disease or in conditions where fibrin breakdown products are increased.
Clinicians order this test when you have unexpected bleeding, an abnormal screening clotting test, or when they need to evaluate the influence of medications such as heparin or direct thrombin inhibitors. Results guide whether additional tests are needed, whether medicines are contributing, and what treatments or precautions are appropriate.
If your Thrombin Time is longer than expected, your clinician will review your medications, especially heparin and direct thrombin inhibitors, and consider issues with fibrinogen amount or function. They may compare this result with related tests, such as reptilase time and fibrinogen activity, to distinguish a drug effect from a fibrinogen problem or interference from fibrin breakdown products.
A normal Thrombin Time makes significant heparin or direct thrombin inhibitor effects less likely, but it does not exclude all causes of bleeding. If results are unexpected, your team may repeat testing to rule out specimen problems, perform mixing studies, check kidney or liver function, or screen for conditions like disseminated intravascular coagulation. Your individual situation, symptoms, and medicines guide the next steps.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Blood drawn from or through heparinized lines can falsely prolong the Thrombin Time. Drawing from a clean peripheral vein and discarding the first few milliliters when needed helps avoid this issue.
Medicines that directly inhibit thrombin, such as dabigatran or parenteral agents, can markedly prolong the result. Timing of the last dose, kidney function, and drug level influence the degree of effect.
Low fibrinogen or inherited or acquired dysfibrinogenemia slows clot formation. Liver disease, massive bleeding, or consumption in critical illness can reduce functional fibrinogen and prolong the test.
Underfilled citrate tubes, clotted samples, delays to testing, or improper storage temperature can alter clotting times. Proper fill volume, prompt processing, and correct transport are important.
High levels of fibrin split products or certain abnormal proteins in the blood can interfere with fibrin polymerization, leading to a prolonged result despite adequate fibrinogen levels.
Reduced kidney function can increase exposure to some anticoagulants that affect this test, while liver impairment can lower fibrinogen production. Both situations may prolong the Thrombin Time.
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