**5. Glycosylated hemoglobin (HbA1c)**

Hemoglobin that has been glycosylated (also known as hemoglobin A1c, or HbA1c) is one type of hemoglobin (Hb) that is primarily evaluated to determine the average blood glucose level over a long period of time. This protein is created by hemoglobin's regular exposure to plasma glucose in a gradual, nonenzymatic glycation reaction [79]. Hemoglobin that has been irreversibly glycosylated at either or both of the amino-terminal valines (Val) of the beta-polypeptide chains is referred to as glycosylated hemoglobin [80]. The most widely used and widely approved test for assessing the glycemic management of people with diabetes is HbA1c. Red blood cells (RBCs) retain the glycated form of hemoglobin (Hb) for the duration of the RBC's existence [81]. In clinical settings, HbA1c is employed to precisely reflect glycemic management over the previous (120 days). For individuals without diabetes, the optimal HbA1c test range is often less than 7%; for those with diabetes, the usual range is between 4 and 6%. [82]. The test can be taken at any time of day and requires no special preparation, such as fasting. These characteristics have made it the best test for assessing diabetics' glycemic control. The American Diabetes Association (ADA) now advises using HbA1c as a diagnostic test for diabetes as there has been much interest in doing so in recent years.

As a method for identifying those with a high risk of getting diabetes [83]. Furthermore, nephropathy and retinopathy in diabetes mellitus have been connected to hemoglobin glycosylation. Since its introduction in clinical settings in the 1980s, HbA1c has been a standard test for determining average plasma glucose over the preceding 8 to 12 weeks.

The relationship between HbA1c percent and plasma glucose levels is well recognized; the higher blood glucose levels, the higher the level of HbA1c percent, which is useful for monitoring and management; also, as HbA1c percent rises, the risk of complications from diabetes tends to rise. HbA1c% is a helpful indicator of how well plasma glucose level has been controlled recently and can be used to track the effects of exercise, diet, and medication therapy on plasma glucose in diabetic patients because HbA1c levels are unaffected by daily variations in plasma glucose levels and instead reflect average glucose levels over the prior 6 to 8 weeks [84]. The best tool available to doctors to assess the overall management of diabetes is HbA1c% as a consequence [85].

#### **5.1 Insulin**

A hormone produced in the pancreas is insulin (an organ located behind the stomach). Islets, or cell clusters, are found in the pancreas. Insulin is produced by beta cells within the islets and released into the circulation. In metabolism, insulin is important [86]. It is a key anabolic hormone that is secreted in response to increased amino acid blood and glucose followed by ingestion of a meals. Similar to many hormones, insulin works by attaching to certain receptors on the body's cells, including those in the fat, muscle, and liver cells [87]. Insulin's primary function is to promote the absorption of glucose. **Figure 5** shows the two polypeptide chains that make up the protein insulin: A (21 amino acid residues) and B (30 amino acid residues). Disulfide bridges connect chains A and B. An intrachain disulfide bridge connecting residues 6 and 11 [89] is also present in the A-chain.

*Carbohydrate Metabolism in Growth Hormone Therapy for Children DOI: http://dx.doi.org/10.5772/intechopen.110778*

**Figure 5.** *Insulin structure [88].*
