Partial Thromboplastin Time (PTT) Test

The Partial Thromboplastin Time (PTT) test, also known as the Activated Partial Thromboplastin Time (aPTT), is a blood test used to evaluate the intrinsic and common coagulation pathways.

Purpose of the Test

The PTT test is used to:

• Assess the coagulation factors in the intrinsic pathway, including factors VIII, IX, XI, and XII.
• Evaluate the common coagulation pathway, which includes factors I, II, V, and X.
• Monitor patients on heparin therapy to ensure that their blood is not too prone to clotting or bleeding.
• Diagnose bleeding disorders, such as hemophilia A and B.

How the Test is Performed

The PTT test involves the following steps:

1. A blood sample is drawn from a vein in the arm or hand.
2. The blood sample is mixed with an anticoagulant to prevent clotting.
3. A chemical called activator is added to the blood sample to activate the intrinsic coagulation pathway.
4. The mixture is then incubated at a specific temperature for a set period of time.
5. The time it takes for the blood to clot is measured, which is known as the partial thromboplastin time.

Normal Results

A normal PTT result typically ranges from 25 to 35 seconds, but this can vary depending on the laboratory and the specific testing method used.

Abnormal Results

An abnormal PTT result may indicate:

• Prolonged clotting time: This can be caused by a deficiency or dysfunction of one or more coagulation factors, such as factor VIII or IX deficiency (hemophilia A or B), or the presence of an inhibitor.
• Shortened clotting time: This can be caused by the presence of a procoagulant substance or an increase in coagulation factors.

Clinical Significance

The PTT test is an important tool for diagnosing and monitoring bleeding disorders, as well as evaluating the effectiveness of heparin therapy. It can also help identify patients who are at risk of bleeding or thrombosis.