Interference from lupus anticoagulant on von Willebrand factor measurement in splenic marginal zone lymphoma: a case report.

We present a case concerning a patient with splenic marginal zone lymphoma (SMZL) and isolated prolonged activated partial thromboplastin time (aPTT) caused by lupus anticoagulant. Von Willebrand factor (VWF) activity and antigen were immeasurable by latex particle immunoturbidimetric assays, and several coagulation factor levels were decreased. However, VWF activity and antigen were normal when analyzed by other methods. Also, coagulation factor levels were normal if an aPTT reagent with low lupus anticoagulant sensitivity or a chromogenic method was applied. Altogether, the initial findings were because of lupus anticoagulant interference and in fact, the patient had normal VWF activity and coagulation status. Interference of lupus anticoagulant in clot-based assays is well known but has not previously been described in VWF assays. This is furthermore the first report in which lupus anticoagulant activity in SMZL cannot be ascribed to a monoclonal immunoglobulin. In our study, aPTT normalized after treatment, suggesting resolution of lupus anticoagulant. APTT could thus be a marker of treatment response in SMZL. Whether treatment decreases the thrombosis risk due to lupus anticoagulant remains unknown.