Glycated hemoglobin (HbA1c) is an important indicator of glycemic control in diabetes mellitus, based on which important diagnostic and therapeutic decisions are routinely made. However, there are several situations in which the level of HbA1c may not faithfully reflect the glycemic control in a given patient. Important among these is the use of certain non-diabetic medications, which can affect the HbA1c levels in different ways.
Normal adult hemoglobin consists predominantly of HbA1, of which HbA1c comprises approximately 5% [4].
However, HbA1c does not always correlate with blood glucose levels. It is possible to have high blood glucose but low HbA1c due to the presence of hemoglobin variants, inflammation, or other factors that increase red blood cell turnover.
After that discovery, numerous small studies were conducted correlating it to glucose measurements resulting in the idea that HbA1c could be used as an objective measure of glycaemic control.
The A1C-Derived Average Glucose (ADAG) study included 643 participants representing a range of A1C levels. It established a validated relationship between A1C and average glucose across a range of diabetes types and patient populations (13). HbA1c was introduced into clinical use in the 1980s and subsequently has become a cornerstone of clinical practice [7].
HbA1c reflects average plasma glucose over the previous eight to 12 weeks. It can be performed at any time of the day and does not require any special preparation such as fasting. These properties have made it the preferred test for assessing glycaemic control in people with diabetes. More recently, there has been substantial interest in using it as a diagnostic test for diabetes and as a screening test for persons at high risk of diabetes
Owing in large part to the inconvenience of measuring fasting plasma glucose levels or performing an OGTT, and day-to-day variability in glucose, an alternative to glucose measurements for the diagnosis of diabetes has long been sought. HbA1c has now been recommended by an International Committee and by the ADA as a means to diagnose diabetes. Although it gives equal or almost equal sensitivity and specificity to a fasting or post-load glucose measurement as a predictor of prevalent retinopathy, it is not available in many parts of the more recently in the DETECT-2 analysis Overall, the performance of HbA1c has been similar to that of fasting or 2-h plasma glucose.
For all three measures of glycaemia, the value above which the prevalence of retinopathy begins to rise rapidly has differed to some extent between studies. Although HbA1c gives equal or almost equal sensitivity and specificity to glucose measurement as a predictor of prevalent retinopathy, it is not available in many parts of the world, and in general, it is not known which is better for predicting microvascular complications. World. Also, many people identified as having diabetes based on HbA1c will not have diabetes by direct glucose measurement and vice versa.
The relationship between HbA1c and prevalent retinopathy is similar to that of plasma glucose, whether glucose and HbA1c are plotted in deciles in vigintiles or as continuous variables. This relationship was originally reported in the Pima Indians and has also been observed in several other populations including Egyptians, the NHANES study in the USA in Japanese