Citrated human blood containing 10% glycerol, or 10% dextrose, or no additive, was frozen in capillary tubes at cooling rates ranging from 1 to 15,000°C per min to a temperature of -100°C and then stored in liquid nitrogen. The frozen blood was thawed rapidly, and the extent of injury to the erythrocytes was measured by a colorimetric determination of the amount of hemoglobin released from the damaged cells. The results obtained indicate that there is a definite range of cooling rates at which minimum hemolysis occurs and that this effective range varies depending upon the presence and nature of protective additives as follows: 1) in blood without additive minimum damage occurs at cooling rates of 1,600 to 3,500°C per min; 2) in blood containing 10% glycerol minimum injury is obtained with cooling rates of 5 to 150°C per min; and 3) although 10% dextrose in blood reduced hemolysis over the entire range of cooling rates investigated, minimum injury is obtained at rates of the order of 2,300 to 3,500°C per min. Cooling rates above and below these ranges cause an increase in lysis. These results confirm previous findings, in which blood was frozen at various rates by immersion to baths at different temperatures, that the effective factor in preventing or causing hemolysis is the cooling rate and not the final temperature. © 1968.
