The initial workup of a prolonged PTT is a mixing test whereby the patient's plasma is mixed with normal pooled plasma and the clotting is reassessed. If a clotting inhibitor such as a lupus anticoagulant is present, the inhibitor will interact with the normal pooled plasma and the clotting time will remain abnormal. However, if the clotting time of the mixed plasma corrects towards normal, the presence of an inhibitor such as the lupus anticoagulant is excluded, and instead a deficient quantity of clotting factor (that is replenished by the normal plasma) is likely.