[Extreme pseudoagglutination of the red blood corpuscles by cold-labile IgM paraprotein (author's transl)].

Electronic cell count and blood smear was impossible because of extreme pseudoagglutination of erythrocytes in a 70-year-old woman with chronic lymphoid leukaemia and associated antibody deficiency. Cold precipitation of citrated plasma occurred at 4 degrees C, turbidity was noted at room temperature, and the plasma was clear at 37 degrees C. Serum immunoelectrophoresis demonstrated IgM paraprotein of kappa type which was also present in the eluate after breaking up the erythrocyte surface at 37 degrees C. This demonstrates that the pseudoagglutination was caused by loading of the red blood corpuscles by a serologically defined cryoglobulin.