Erythrocyte aggregation--determination of normal values. Influence of age, sex, hormonal state, oestroprogestative treatment, haematological parameters and cigarette smoking.

Erythrocyte aggregation is a physiological phenomenon and constitutes one of the most important factors accounting for the non-Newtonian properties of normal human blood. Pathological aspects have also been described and therapy aimed at reducing hyperaggregability has been proposed. The object of this study was to establish normal values of erythrocyte aggregation parameters as measured by laser light backscattering and to study the influence of various physiological factors. Normal values were determined from a reference population. Sex and age induce variations in erythrocyte aggregation which are neither fibrinogen nor haematocrit dependent and there is a general trend towards stronger aggregation in women, although neither hormonal state nor oestroprogestative treatment appear to influence the female aggregation parameters. In elderly people stronger aggregation is also observed but this effect is of lower magnitude. In vivo, the plasma fibrinogen level is the most important factor influencing erythrocyte aggregation, while variations in haematocrit play a lesser role and mean corpuscular volume, red cell distribution width and white blood cell and platelet counts have no effect. Finally, no difference is noted in cigarette smokers.