Glycosolated Hemoglobin

Description
Measured by the HbA1c test, Glycosolated Hemoglobin is a measure of the amount of sugar that is attached to the hemoglobin in red blood cells (http://www.nlm.nih.gov/medlineplus/ency/article/003640.htm). The results are reported as a percentage. People without diabetes usually have a result of about six percent in this test. Because red blood cells live in the bloodstream for approximately four months, the HbA1c test shows the average blood sugar for the past 2 to 3 months and is an indicator of glucose metabolism over that time.
Unlike other blood sugar tests, the HbA1c test is not affected by short-term changes. Glycosylated hemoglobin can be a good measure of how well diabetes is managed over time (http://www.nlm.nih.gov/medlineplus/ency/article/003640.htm).

Significance of Measurement
Higher test values are associated with higher risk of complications from diabetes (eye disease, kidney disease, nerve damage, heart disease, and stroke) (http://www.nlm.nih.gov/medlineplus/ency/article/003640.htm). Only a small percentage of the hemoglobin molecules in red blood cells become glycosylated (that is, chemically linked to glucose). The percent of glycosylation increases over time and increases with more glucose in the blood. Therefore, older red blood cells will have a greater percent of glycosylated hemoglobin, and diabetics whose blood glucose has been too high will have a greater percent of glycosylated hemoglobin (http://www.nlm.nih.gov/medlineplus/ency/article/003640.htm).
Levels of glycosylated hemoglobin indicating poor glycemic control among diabetics have been related to poor cognitive function in some studies (Reaven et al., 1990; Gradman et al., 1993; Perlmuter, 1984; Jagusch et al., 1992). However, no such association was observed in other studies (Worrall et al., 1993; Lowe et al. 1994).

Method of Measurement
Glycosylated hemoglobin can be assayed from blood samples or blood spots.

References
· Gradman, T.J., Laws, A., Thompson, L.W., & Reaven, G.M. (1993). Verbal learning and/or memory improves with glycemic control in older subjects with non-insulin dependent diabetes mellitus. Journal of the American Geriatrics Society, 41, 1305–1312.
· Jagusch, W., Cramon, D.Y.V., Renner, R., & Hepp, K.D. (1992). Cognitive function and metabolic state in elderly diabetic patients. Diabetes Nutrition and Metabolism, 5, 265–274.
· Lowe, L.P., Tranel, D.T., Wallace, R.B., & Welty, T.K. (1994). Type II diabetes and cognitive function. Diabetes Care, 17, 891-896.
· Perlmuter, L.C., Hakami, M.K., Hodgson-Harrington, C., Ginsberg, J., Katz, J., Singer, D.E., et al. (1984). Decreased cognitive function in aging non-insulin-dependent diabetic patients. American Journal of Medicine, 77, 1043–1048.
· Reaven, G.M., Thompson, L.W., Nahum, D., & Haskins, E. (1990). Relationship between hyperglycemia and cognitive function in older NIDDM patients. Diabetes Care, 13, 16–21.
· U.S. National Library of Medicine & National Institutes of Health. (2003). medline plus: Trusted health information for you. Retrieved March 28, 2005, from http://www.nlm.nih.gov/medlineplus/ency/article/003640.htm
· Worrall, G., Moulton, N., & Briffett, E. (1993). Effect of type II diabetes mellitus on cognitive function. Journal of Family Practice, 36, 639–643.