The effect of anticoagulant on platelet associated IgG

Blood anticoagulated with solid K2EDTA had platelet associated IgG (PAIgG) levels five-fold greater than citrated blood when the platelets were harvested by differential centrifugation but identical PAIgG levels when the platelets were harvested by Percoll density gradient. Furthermore, blood anticoagulated with increasing amounts of solid K2EDTA demonstrated a proportionate increase in both PAIgG and haemolysis whereas the same blood sample anticoagulated with aqueous K2EDTA exhibited neither of these effects. Coulter Counter analysis of platelet poor plasma (PPP) prepared from blood anticoagulated with solid K2EDTA revealed particles with a mean volume greater than normal RBC; such particles were not found in the PPP prepared from citrated blood. While some of these particles could be sedimented through plasma, those remaining were sufficiently buoyant to resist sedimentation unless the plasma was diluted with buffer. Studies with FITC conjugated antisera revealed that the particles could be classified into two types. Type I particles reacted strongly with a monoclonal anti-RBC antibody, weakly with anti-IgG antibody and had the appearance of stroma. Type II particles lacked any apparent biological structure, reacted strongly with anti-IgG antibody but not with monoclonal anti-RBC antibody. Thus, the buoyant IgG-rich particles found in blood anticoagulated with solid K2EDTA appear to contribute to the high PAIgG levels associated with this anticoagulant. Consequently, solid K2EDTA should not be used to anticoagulate blood destined for PAIgG measurement.