Effects of plasma osmolality on red cell size

The changes in plasma osmolality and percentage change in mean corpuscular volume accompanying dehydration (2~ and 4of body weight loss) were studied to assess the use of the venous hematocrit as a gauge of the percentage change in plasma volume. In vitro experiments were also conducted to verify the relationship between plasma osmolality and mean corpuscular volume.By utilizing the mean corpuscular hemoglobin concentration, calculation of the percentage change in mean corpuscular volume following dehydration showed a marked shrinkage of the red cells that was significantly related to the increase in plasma osmolality (r = - 0.99). Consequently, it was concluded that calculations of the percentage change in plasma volume during dehydration based on the change in venous hematocrit are subject to error unless corrections are made for alterations in mean corpuscular volume.Ball State UniversityMuncie, IN 47306