Specific Gravity of Blood and Plasma at 4 and 37 °C

Abstract The specific gravity (relative density) of human whole blood and plasma from 25 healthy volunteers was determined gravimetrically. For whole blood it was found to be 1.0621 (95% confidence interval: 1.0652-1.0590) at 4 °C and 1.0506 (95% confidence interval: 1.0537-1.0475) at 37 °C. Plasma specific gravity was 1.0310 (95% confidence interval: 1.0324-1.0296) at 4 °C and 1.0205 (95% confidence interval: 1.0216-1.0193) at 37 °C. All of these values are referred to the density of water at 4 °C. We show the relationship between these values and those given in the literature for measurements at 25 °C. There was a small increase in whole blood specific gravity with increasing hematocrit, but it was not statistically significant over the 40-56 hematocrit range studied.