Intercellular Plasma of Centrifuged Human Erythrocytes as Measured by Means of Iodo131-Albumin

Abstract

The volume of packed red cells was detd. on samples of heparinized venous blood from 39 men and women. Simultaneously the plasma volume was calculated by the addition of radioactive iodo131-albumin to these samples of blood. It was assumed that none of the albumin prepn. attached to or entered the erythrocytes. The volume of red cells as estimated by the iodo131-albumin method was smaller than that obtained by the centrifugal hematocrit method in 37 of the 39 samples, the mean difference being 1.7 percentage units. When the difference between the 2 methods was expressed as a percentage of the centrifugal hematocrit value, the mean value was 3.79 + 0.70%; i.e., slightly less than 4% of the cell volume as detd. by centrifugation consists of trapped plasma. Unequal trapping of plasma in various portions of packed red cells introduces an error into attempts to measure trapped plasma by "direct" methods.