Geometry of neonatal and adult red blood cells.

Red blood cell (RBC) geometry is a determinant of RBC deformability, survival time, osmotic resistance, and oxygen uptake. Because accurate information on the geometry of neonatal RBC appears lacking, a micropipette technique was employed to measure surface area and volume of individual neonatal and adult RBC. In addition, RBC diameter was determined microscopically. From these measurements, surface area index (actual surface area divided by area of sphere of same volume), swelling index (maximal volume divided by actual volume), minimum cylindrical diameter and mean thickness of RBC were calculated. Compared to adult cells, the volume of neonatal RBC was 21% larger, their surface area was 13% greater and their diameter 11% wider. The surface area-to-volume ratio of the neonatal RBC was 1.42 +/- 0.08 and that of the adult RBC was 1.49 +/- 0.06 (P less than 0.05). The minimum cylindrical diameter of the neonatal RBC was 3.04 +/- 0.25 microns and that of the adult RBC was 2.81 +/- 0.23 microns (P less than 0.05). Mean RBC thickness, surface area index and swelling index were not significantly different.