Density increase and ageing of erythrocytes in stored blood.

An increase in the density of erythrocytes was observed after storage of whole blood for 30 days at 4 degrees C in either acid citrate-dextrose or citrate-phosphate-dextrose-adrenaline. Glucose-6-phosphate dehydrogenase activity in unfractionated red blood cell lysates did not vary with the storage time. Enzyme activity in the lighter fraction separated by density gradient centrifugation was higher than that in heavier fractions. The decline in glucose-6-phosphate dehydrogenase activity with density was less marked after storage of whole blood for 30 days. It is suggested that density modifications are not related to the ageing of erythrocytes and additional mechanisms may be involved.