Clinical Nutrition

Lesson 25: Diabetes Mellitus- Complications and Insulin

Glycosylated Hemoglobin A 1C

• Another blood test used for diabetes screening and monitoring is that of glycosylated haemoglobin (Hb A 1 C)
• This test is based on the fact that a condensation reaction occurs between glucose and the amino acids in a protein without enzymatic action. In the body, various proteins, like haemoglobin and serum albumin are thus glycosylated. In diabetes glycosylation is related to the magnitude and duration of hyperglycemia.
• The sugar content of haemoglobin is normally less than 6% but in poorly controlled diabetes this value can exceed 25%. The bond between glucose and haemoglobin in erythrocytes can be easily dissociated under normal conditions. But on prolonged exposure to high glucose concentrations the bond becomes irreversible and the linkages formed remain till the cell is degraded.
• Thus levels of glycosylated haemoglobin reflect glycemic control over the previous 6-8 weeks.
• In patients with excellent glycemic control the values are normal. Poor diabetic control yields values exceeding 90%.
• Glycosylation in excess contributes to vascular permeability, microcirculation defects and functional abnormalities of erythrocytes.