Partial thromboplastin time

Partial Thromboplastin Time (PTT) is a blood test used to assess the body's ability to form blood clots. It measures the time it takes for a clot to form in a sample of blood after substances (reagents) are added. The test is used to monitor the effectiveness of anticoagulant therapy and to diagnose bleeding disorders.

Procedure

The PTT test is performed by drawing blood from a vein, usually in the arm. The blood is then mixed with reagents in a test tube and the time it takes for a clot to form is measured. The normal range for PTT is typically between 25 and 35 seconds, but this can vary depending on the laboratory that analyzes the sample.

Clinical Significance

PTT is used to monitor patients who are on heparin, a type of anticoagulant medication. It can also be used to diagnose conditions that affect the clotting process, such as hemophilia and von Willebrand disease. A prolonged PTT can indicate a deficiency in one or more clotting factors, while a shortened PTT can suggest an increased risk of clotting.

Limitations

While PTT is a useful test, it has some limitations. It is not sensitive to all clotting disorders, and it can be affected by factors such as the patient's diet and medication use. Additionally, the test requires a relatively large volume of blood, which may not be feasible for some patients.

See Also

• Prothrombin time
• International normalized ratio
• Coagulation

Partial thromboplastin time

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  Diagram of the coagulation cascade
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  Blue top tube used for coagulation tests