Long-term storage of blood samples at freezing temperatures in the presence of a cryoprotectant for hemiglobin assay.

Changes in Hi levels in experimentally prepared blood samples during storage at various temperatures were studied. When whole blood in which Hi levels were elevated by sodium nitrite was stored unfrozen, rapid reduction of Hi was observed within 24 hr even at 0 degrees C. When whole blood or a diluted hemolysate was stored frozen for a week or longer, considerable formation of Hi by autoxidation was observed, the formation at -20 degrees C being much more significant than that at -30 degrees C. On the other hand, addition of an equal volume of the cryoprotectant solution of Rowe et al. to blood almost completely inhibited this Hi formation during freezing storage until at least 30 days. Thus, a new method for long-term storage of blood samples for Hi assay was devised.