Pseudoleukocytosis without pseudothrombocytopenia induced by the interaction of EDTA and IgG(2)-kappa M-protein

We encountered a patient who showed ethylenediaminetetraacetic acid (EDTA)-induced pseudoleukocytosis without pseudothrombocytopenia. The patient had IgG-kappa type monoclonal (M) gammopathy. The total protein concentration was 77 g/l, and the gamma-globulin fraction containing M-protein was 23.2%. The white blood cell count of the patient's blood anti-coagulated with EDTA was 52300/microl as determined using an automated counter, but was within normal limits when counted manually by light microscopy using a hemacytometer. Large amounts of a transparent substance were observed on blood smears, and white precipitates were formed by an interaction of the patient's serum with EDTA. Immunofixation electrophoresis showed these precipitates to be of the IgG(2)-kappa type M-protein. Western blotting analysis showed that the IgG molecules had a molecular mass of 155 kDa and were composed of two gamma-chains of approximately 53 kDa and two kappa-chains of 27 kDa. Pseudoleukocytosis was also observed when the patient's blood was anti-coagulated with O, O'-bis(2-amino-ethyl)-ethyleneglycol-N,N,N',N'-tetraacetic acid (EGTA) or sodium citrate, but not with lithium heparin. The present case seems to be the first report of pseudoleukocytosis induced by the interaction of EDTA and IgG(2)-kappa type M-protein.