What is measured by activated partial thromboplastin time (aPTT) testing?

Activated partial thromboplastin time (aPTT) testing is specifically designed to evaluate the intrinsic and common coagulation pathways of the blood coagulation process. This test involves measuring the time it takes for blood to clot after a series of reagents are added, which activates the intrinsic pathway.

The intrinsic pathway is primarily responsible for initiating the coagulation cascade when there is vascular injury. The common pathway, which overlaps with both the intrinsic and extrinsic pathways, is characterized by the activity of certain clotting factors that eventually lead to the formation of a fibrin clot.

By assessing the aPTT, healthcare providers can identify abnormalities in these pathways, which can indicate various bleeding disorders, the efficacy of certain anticoagulant therapies, and can help monitor patients with hemophilia or those undergoing complex surgeries requiring hemostatic management.

This testing does not measure the effectiveness of the extrinsic pathway, nor does it assess genetic factors related to hemophilia or overall blood viscosity, which further cements its specific focus on the intrinsic and common pathways in the coagulation process.