Factor X, also known as Stuart-Prower factor, is a crucial protein in the blood clotting process. It is involved in the common pathway of coagulation, where it gets activated to Factor Xa, which then helps convert prothrombin to thrombin, leading to the formation of a blood clot. The Factor X test measures the activity or levels of this clotting factor in the blood.

Low levels of Factor X can lead to bleeding disorders, while high levels may increase the risk of thrombosis (abnormal clotting). The test is typically used to diagnose clotting deficiencies or to monitor anticoagulant therapy, particularly in patients with unexplained bleeding or clotting events.