Which test would be abnormal in a patient with factor X deficiency?

In a patient with factor X deficiency, both the prothrombin time (PT) and activated partial thromboplastin time (APTT) would be abnormal. Factor X is a crucial component in the coagulation cascade, affecting both the intrinsic and extrinsic pathways of blood coagulation.

The prothrombin time assesses the extrinsic pathway, primarily involving factors I (fibrinogen), II (prothrombin), V, VII, and X. A deficiency in factor X directly impacts this pathway, resulting in an increased PT due to insufficient thrombin generation.

Similarly, the activated partial thromboplastin time evaluates the intrinsic pathway, which includes factors I, II, V, VIII, IX, X, XI, and XII. A deficient factor X would also prolong the APTT because this factor is essential for the conversion of prothrombin to thrombin, which is necessary for the common pathway of coagulation that includes both extrinsic and intrinsic factors.

Thus, a patient with factor X deficiency would show abnormalities in both PT and APTT, leading to the conclusion that the correct answer is that both tests would be affected. Other tests such as the thrombin time are not directly impacted by factor X deficiency and typically