Which clotting factors are measured by the APTT test?

The activated partial thromboplastin time (APTT) test is primarily used to evaluate the intrinsic pathway of coagulation and the common pathway. This test measures the time it takes for blood to clot after adding specific reagents that activate the intrinsic pathway factors.

The correct answer encompasses the full range of clotting factors involved in both the intrinsic and common pathways, specifically factors XII, XI, IX, VIII, X, V, II (prothrombin), and I (fibrinogen). Each of these factors plays a crucial role in the coagulation cascade. For example, factors VIII and IX are critical in the intrinsic pathway, with factor VIII being a cofactor for factor IXa in the conversion of factor X to Xa, while factor II (prothrombin) is necessary for the final conversion to fibrin.

The inclusion of factors like IX and VIII reflects the test's sensitivity to conditions such as hemophilia, which arises from deficiencies in those specific factors. Thus, the comprehensive nature of the APTT test is highlighted by the measurement of these factors, supporting its use in diagnosing various bleeding disorders.

This understanding clarifies its relevance in clinical practice, especially in assessing the coagulation disorders that may not be identified through