Long-term storage of blood samples as whole blood at extremely low temperatures for methemoglobin determination.

Changes in methemoglobin (Met-Hb) concentrations during storage of whole blood and a hemolysate at refrigerated or various freezing temperatures were examined using experimentally prepared blood samples. When whole blood was stored at 3 degrees C, rapid reduction of Met-Hb was observed in the nitrite-treated blood whereas neither reduction nor formation of Met-Hb was observed in the untreated and heated blood within 7 days. When hemolysate was stored at 3 degrees C, Met-Hb concentrations were stable within a few days regardless of the initial values. However, slight autoxidation was observed 7 days after storage in the untreated and heated blood. When whole blood was stored at various freezing temperatures, Met-Hb concentrations were practically stable until at least 30 days at -80 degrees C or -196 degrees C regardless of the initial values, although considerable autoxidation was observed at -30 degrees C especially in the blood containing small amounts of Met-Hb. Based on the results obtained, a new method was devised for long-term storage of whole blood at extremely low temperatures for Met-Hb determinations.