tokens: In order to study the influence of iron overload on the polymorphonuclear leucocyte ( PMN ) metabolism of patients on chronic hemodialysis , generation of superoxide anion ( O2 - ) by PMN in whole blood was compared in two groups of hemodialyzed patients : group A consisted of twenty - one individuals with serum ferritin levels above 1000 ng / ml and group B of nineteen individuals with serum ferritin levels below 1000 ng / ml .