Red blood cell aggregation and sedimentation: the role of the cell shape

The influence of erythrocyte shape changes on the sedimentation rate was studied in vitro and in vivo. In vitro the highest sedimentation rate was observed with a slight degree of stomatocytosis (morphological index-0.3; i.e. one red cell out of three being a stomatocyte I). With increasing degrees of stomatocytosis the sedimentation rate gradually decreased. Echinocytosis reduced the aggregation and sedimentation very drastically; the sedimentation rate was virtually zero when echinocytosis I or higher degrees were present. The influence of abnormal cell shapes occurring in vivo was studied in patients with an abnormal blood smear. It was found that a severely abnormal red cell morphology reduced the sedimentation rate in a standardized, fibrinogen-rich plasma to about half. These results indicate that the shape plays a crucial role in the aggregation and sedimentation of red cells and they may contribute to the understanding of the interaction of red cells with other cells such as endothelium.