Abstract: A method of treating of glycosylated hemoglobin and in particular the process of hemoglobin isolation and preparation of a stable glycosylated hemoglobin in which the glycosylated hemoglobin remains liquid. The method comprises steps including separating human red blood cells from anti-coagulated blood, washing the human red blood cells with physiological saline and centrifuging the red blood cells and aspirating and discarding a resulting supernatant and white blood cell layer, lysing the packed red blood cells, mixing and freezing the cell/water mixture, defrosting, centrifuging, filtering and saving the supernatant, heating the supernatant, diafiltering the adjusting the hemolysate so that a final hemoglobin concentration is within specified limits. Additives may include potassium cyanide, carbon monoxide, and appropriate preservatives.