What does APTT measure in terms of blood coagulation factors?

The Activated Partial Thromboplastin Time (APTT) is a laboratory test that evaluates the intrinsic and common pathways of blood coagulation. It specifically measures the time it takes for blood to clot in the presence of activated partial thromboplastin and assesses the functionality of several clotting factors.

The intrinsic pathway primarily involves factors 8, 9, 11, and 12. These factors play crucial roles in initiating the clotting cascade once the integrity of blood vessels is compromised. When there is a deficiency or dysfunction in any of these intrinsic pathway factors, the APTT will be prolonged, indicating potential bleeding disorders.

In the context of this question, the correct answer identifies factors specifically associated with the APTT measurement, which are factors 8, 9, 11, and 12, confirming its relevance to the intrinsic pathway of coagulation. This highlights the APTT's role in diagnosing conditions related to these specific coagulation factors, distinguishing it from factors measured by other tests or pathways.