Which factor assay is related to determining the presence of circulating anticoagulants?

The mixing study is a crucial assay used to determine the presence of circulating anticoagulants, such as lupus anticoagulants or other inhibitors of the clotting factors. In this procedure, a patient’s plasma is mixed with normal plasma. If the patient has a circulating anticoagulant, the clotting time will remain prolonged, indicating that an inhibitor is present. This is because the anticoagulant interferes with the normal clotting factors even when they are provided by the normal plasma.

In contrast, if there were no inhibitors present, the mixing would correct the clotting time back to normal, as the normal plasma's factors would compensate for any deficiencies in the patient’s plasma. This ability to gauge the presence of inhibitors in the coagulation cascade makes the mixing study an essential tool in the hematology laboratory for diagnosing certain coagulation disorders.