Separation and characterization of red blood cells from newborns and infants during the first trimenon of life by means of a dextran density gradient. Density distribution curves of erythrocytes and reticulocytes.

Longitudinal studies on the density of erythrocytes and reticulocytes were performed by means of the isopyknic density gradient centrifugation in dextran on three mature newborns and six premature infants during the first 3 months of life. Striking changes of the density distribution curves of red blood cells took place during the first trimenon. Median density (D50) reached its maximum between the 7th and 28th day of life. D50 of reticulocytes was lower than that of the total red blood cell population and shows similar changes to the whole cell population during the first trimenon after birth. Based on the close relationship between D50 and the percentage of lightest cells, the evaluation of the percentage of the lightest cells was recommended as a simple test to study the changes in median density.