When many people with diabetes go to the hospital for a checkup, their doctor will order a glycosylated hemoglobin test. Glycated hemoglobin (or the related glycosylated hemoglobin test) measures the average level of your blood sugar over the past few months. The average lifespan of a red blood cell is 120 days; the old red blood cells then break down, mainly in the spleen, and some of these break down to participate in the production of red blood cells again. The amount of glucose that sticks to the glycated hemoglobin in red blood cells during their 120-day life depends on how high or low your average blood glucose level has been over the past 120 days. Note the meaning of the word average. Not everyone’s red blood cell life span is exactly 120 days. There is some variation due to different people’s physiology. Other influencing factors are temporary illnesses, medications, etc. Any condition that reduces the lifespan of red blood cells can lower the glycated hemoglobin measurement. These factors include hemolytic anemia (a type of anemia caused by ruptured red blood cells), massive blood loss due to an accident or blood donation, hemochromatosis, persistent fever, or a genetic abnormality. Conversely, any condition that increases the lifespan of red blood cells can increase the glycated hemoglobin measurement. One such factor is after spleen removal, as the spleen is the primary place where aging, degenerating red blood cells break down. Genetic abnormalities can also increase the lifespan of red blood cells. So, if your glycated hemoglobin results don’t seem to match your daily measured blood glucose levels, ask your doctor if he can find some factors that can affect the lifespan of your red blood cells. But, wait a minute! There are some other influencing factors. Remember that glycated hemoglobin assesses the average blood glucose level over the past few months. This average has nothing to do with how high or low your blood sugar has been in the past. If your blood glucose level was around 11.1mmol/L (200mg/dl ) for half of the time and 2.8mmol/L (50mg/dl) for the other half, your average blood glucose is 6.9mmol/L (125mg/dl ) ((200+50)/2), so your glycosylated hemoglobin result is consistent with your blood glucose remaining at 6.9mmol/L (125mg/dl ) for most of the time. The latter is a rare condition because blood glucose fluctuates in non-diabetics as well, but it is easier to understand when described this way). For some diabetics, blood glucose is like a roller coaster ride, going very high this hour and very low an hour later, with consequences that are quite different from those of lesser blood glucose fluctuations. Blood sugar fluctuations can cause symptoms of high blood sugar in one hour and low blood sugar in the next. They cause the osmotic pressure in your lens to change constantly, leading to fluctuations in vision. And some people find that constantly fluctuating blood sugar can make them feel hungry. In addition, highly fluctuating blood sugar affects the walls of blood vessels, promoting the development of atherosclerosis. Remember that your glycated hemoglobin results indicate only your average blood sugar levels over the past few months. You still need to have your blood sugar tested daily to know how your blood sugar fluctuates after diet and exercise.