Effect of hemolysis on apparent values of platelet-associated IgG

Addition of red blood cells hemolyzed in the presence of dilute plasma in quantities equivalent to as little as 0.2% hemolysis of red blood cells in whole blood caused significant elevation in the apparent value of IgG associated with platelets (PAIgG) isolated from the preparation. Addition of hemolysate to plasma containing low concentrations of platelets, simulating that obtained from thrombocytopenic patients, caused more striking elevations in apparent PAIgG. Centrifugation of platelet-rich plasma containing hemolysate through a 30% solution of Percoll restored the value of PAIgG essentially to normal. Additional studies using simulated patient whole blood samples anticoagulated with EDTA yielded similar results. The apparent elevation of PAIgG in these preparations appears to result from IgG-bearing membranous material and microspherocytes that co-isolate with platelets separated from blood by conventional methods. Caution should be used in interpreting the results of PAIgG measurements on platelets isolated from blood samples in which even minimal in vitro hemolysis has occurred.