Activated Partial Thromboplastin Time (aPTT) Test

The activated partial thromboplastin time (aPTT) test is a blood test that measures the time it takes for blood to clot. It is used to evaluate the intrinsic and common coagulation pathways.

Purpose of the Test

The aPTT test is used to:

• Monitor patients on heparin therapy, as heparin can affect the intrinsic coagulation pathway
• Diagnose bleeding disorders, such as hemophilia A and B
• Evaluate the effectiveness of anticoagulant therapy
• Investigate the cause of unexpected bleeding or thrombosis

How the Test is Performed

To perform the aPTT test, a blood sample is drawn from a vein in the arm. The blood is then mixed with an anticoagulant to prevent clotting. The sample is then incubated at 37°C and an activator is added to initiate the coagulation process.

Interpretation of Results

The results of the aPTT test are reported in seconds. A normal range for aPTT is typically between 25-35 seconds, but this can vary depending on the laboratory and the specific testing method used.

• A prolonged aPTT result may indicate:
• Heparin therapy
• Hemophilia A or B
• Other bleeding disorders, such as factor XI deficiency
• Lupus anticoagulant or other antiphospholipid antibodies
• A shortened aPTT result may indicate:
• Hypercoagulability, which can increase the risk of thrombosis
• Certain types of cancer, such as pancreatic cancer

Limitations and Interferences

The aPTT test can be affected by various factors, including:

• Hemolysis or lipemia in the blood sample
• Certain medications, such as heparin, warfarin, and aspirin
• High levels of triglycerides or bilirubin
• Certain medical conditions, such as liver disease or kidney disease

Reference Range

The reference range for aPTT can vary depending on the laboratory and the specific testing method used. It is essential to consult with a healthcare professional to interpret the results of an aPTT test.