Abstract: To investigate the role of red blood cell (RBC) geometry in determining the filterability of stress-induced macrocytes, measurements of RBC volume, diameter, and passage time through 3 micron and 5 micron filters were made on RBCs from control rats and from phenylhydrazine-treated rats during a 28-day recovery period following the peak hemolytic response to the anemia induced by phenylhydrazine (PHZ). Mean cell volumes (MCV) were calculated from volume distribution curves; RBC diameters were obtained from peripheral blood smears; surface area (SA) and mean cylindrical diameter (MCD) were calculated using a biconcave erythrocyte model. At the time of the peak macroreticulocyte response to PHZ, MCD and MCV were significantly increased compared to controls (3.07 vs 2.57 microns, and 102.1 vs 59.7 cubic microns, respectively), the ratio SA/MCV was significantly reduced (1.405 vs 1.670), and RBC filterability through both 3 and 5 micron cylindrical pores was significantly reduced. During the 28-day recovery period, MCV, MCD, SA/MCV, and filterability all returned toward the control values, MCD was inversely correlated with filterability through both 3 micron (r = -0.861, p < .01) and 5 micron (r = -0.767, p < .01) pores, and MCD fell below 3.6 microns in 97.5% of the animals despite the persistence of large macrocytic subpopulations. These results emphasize the correlation between RBC geometry and filterability, and demonstrate that macrocytes with favorable geometry can persist in the circulation for extended periods without remodeling or reduction in size.
