This study documents the presence of significant analytic error due to pseudoleukocyte formation as the result of platelet clumps induced by EDTA anticoagulant. The frequency of this problem is low, and the more severe cases can be recognized by the development of concomitant pseudothrombocytopenia, which triggers platelet alarms in the instrument. Analytic error may be avoided by analyzing blood drawn by fingerstick or into heparin.