The term HbA1c refers to glycosylated hemoglobin. It develops when hemoglobin, a protein found in red blood cells that carry oxygen throughout the body, binds to blood glucose and glycosylates. The analysis of the levels of glycosylated hemoglobin (HbA1c) provides evidence of the average blood glucose during the previous two or three months, the average life of the red blood cells (red blood cells). ) HbA1c is now recommended as a standard for assessing and controlling diabetes. Historically, HbA1c was isolated for the first time by Huisman in 1958 and characterized by Bookchin and Gallop in 1968 as a glycoprotein. High levels of HbA1c in diabetic patients were reported by Rahbar in 1969. Bunn et al. He identified the path that leads to the formation of HbA1c in 1975. The use of HbA1c as a biomarker to control glucose levels in patients with diabetes was suggested by Koenig et al. In 1976. Proteins are often glucosed during various enzymatic reactions when conditions are physiologically positive. However, in the case of hemoglobin, glycation is produced by non-enzymatic reaction between the glucose and the N-terminal end of the ? chain, which forms the basis of the shif. In the initial phase of glycosylated hemoglobin formation, hemoglobin and blood glucose interact to form a reversible adamin reaction. In the secondary stage, which is irreversible, the indium gradually becomes the stable form of ketoamine. The primary glycosylation sites of hemoglobin, in order of incidence, are ?-val-1, ?-lys-66 and ?-lys-61. Regular adult hemoglobin consists mainly of HbA (?2?2), HbA2 (?222) and HbF (?222) in the composition of 97%, 2.5% and 0.5%, respectively. Approximately 6% of HbA is called HbA1c, which in turn consists of the fractions HbA1a1, HbA1a2, HbA1b and HbA1c, defined by their electrophoretic chromatographic properties. HbA1c is the most common of these fractures, and in health, it represents approximately 5% of the total HbA fraction. As noted above, glucose in an open chain format binds to an N-terminus to form an aldamine before undergoing a rearrangement of Amadori to create a more stable ketoamine. This is a non-enzymatic process that occurs continuously in vivo. The formation of glycosylated hemoglobin is a normal part of the physiological function cycle. However, as the average glucose levels increase, the amount of glycosylated hemoglobin plasma also increases. This characteristic of the biological marker of hemoglobin is used to evaluate blood glucose levels during the last two or three months. In this review, we describe current trends in the prevalence, diagnosis and prognosis of diabetes. The HbA1c potential, the analytical aspects of the HbA1c analysis and the physiological changes due to the glycation of hemoglobin.