A prolonged APTT and PT are corrected when mixed with normal plasma. Which factor is most likely deficient?

In this scenario, the presence of prolonged activated partial thromboplastin time (APTT) and prothrombin time (PT) that corrects when mixed with normal plasma indicates that there is a deficiency in a clotting factor that is common to both pathways involved in coagulation.

Both the intrinsic and extrinsic pathways can contribute to APTT and PT prolongation. When the mixing study corrects the clotting times, it suggests that the deficiency is not in the factors already present in the normal plasma because they are able to compensate for the missing factor in the patient’s plasma.

Factor V plays a crucial role in the common pathway of coagulation, where both intrinsic and extrinsic pathways converge. Deficiency of factor V will lead to both PT and APTT being prolonged, and the fact that they both correct upon mixing with normal plasma confirms that the issue lies in a factor that is absent but can be replenished by the addition of normal plasma.

Other factors listed, such as VIII, IX, and XI, are primarily involved in the intrinsic pathway. A deficiency in these would typically lead to a prolonged APTT, but the PT might not be prolonged unless additional complications or factors are involved. Therefore, the most logical conclusion