What test should be performed to determine if the patient has lupus anticoagulant?

The platelet neutralization test is the most appropriate method to determine the presence of a lupus anticoagulant. This test specifically assesses the inhibitory effects of antiphospholipid antibodies, which includes lupus anticoagulants that can prolong coagulation times. In this test, the patient's plasma is mixed with normal platelet-rich plasma, and if the prolongation of the activated partial thromboplastin time (APTT) is corrected, it is indicative of the presence of lupus anticoagulant.

Other tests, such as APTT and prothrombin time (PT), can indicate the overall coagulation status but do not specifically identify lupus anticoagulant. The anti-cardiolipin antibody test measures a different aspect of antiphospholipid syndrome and is not a definitive test for lupus anticoagulant itself. Therefore, the platelet neutralization test stands out as the targeted test needed for diagnosing the presence of lupus anticoagulant.