Assessment of neutrophil aggregation by Coulter STKR and STKS haematological analysers

We have studied an alternative method to aggregometry for the assessment of human polymorphonuclear (PMN) leucocyte aggregation. This simple, rapid and reliable procedure counts unaggregated cells on both Coulter STKS and STKR haematological analysers by the impedance principle. Aggregation of PMN was induced by 15 min incubation with fresh autologous serum (FAS) after a 10 min phorbol myristate acetate (PMA) activation of neutrophils in small aliquots (0.25 ml) of suspension containing about 4.0 x 10(9) PMN/1. Differences (x 100) between count of resting and PMA+FAS treated neutrophils/count of resting PMN reflect percent aggregation. By this procedure, PMN aggregation did not occur in autologous plasma from EDTA anticoagulated whole blood; it was partially inhibited by hydrocortisone, whereas inactivated or Zymosan activated sera gave values similar to those from FAS induced aggregation. PMA aggregation was dependent on Ca2+ + Mg2+ concentration. Intra-assay analytical variability did not exceed 4% on either instrument. Reference values (n = 20) of percent PMN aggregation were 50.7 +/- 4.7 on STKS and 47.1 +/- 4.8 on STKR. Most probably, the interindividual variance was due to the physiological variability of Mg2+ and/or Ca2+ concentrations in FAS. Thus, this procedure reflects the true PMN aggregability status in a given subject, and in a given electrolyte environment.