The Role of HbA1c and Oral Glucose Tolerance Test in the Diagnosis and Differentiation of Prediabetes: Article Review

Abstract

Background: Prediabetes is a condition resulted when the level of glucose is between the normal and hyperglycaemic limits, and it is very important to follow up because it may be developed to diabetes mellitus

It is critical to identify its 2 main phenotypes early and accurately: impaired fasting glucose (IFG) or impaired glucose tolerance (IGT), to prevent us from progressing to type 2 diabetes and its complications. This review is intended to clarify the separate roles of glycated haemoglobin (HbA1c) and the oral glucose tolerance test (OGTT) in diagnosing and discriminating these prediabetic states.

Main body: IFG and IGT result from different pathophysiological processes: IFG is primarily due to hepatic insulin resistance (IR) and also impaired early-phase insulin secretion, while IGT shows prominent peripheral (mainly muscle) IR with defects in both early and late (over the post-prandial period) insulin secretion. The OGTT still provides the gold standard for IGT diagnosis by assessing postprandial glucose excursions. Measurement of HbA1c provides a simple assessment of long-term glycaemia, indicating average glucose level within the previous 2–3 months, and is recommended (5.7–6.4%) by the American Diabetes Association for prediabetes screening. However, its diagnostic utility is limited by several confounding factors (such as anaemias, haemoglobinopathies, and ethnic variations) that contribute to misclassification. FPG, OGTT, and HbA1c identify distinct prediabetic phenotypes with different risk profiles for progression to diabetes and cardiovascular disease. However, it can be diagnosed by performing multiple tests simultaneously, which is very important for increasing diagnostic sensitivity. Both the HbA1c and the oral glucose tolerance test can provide these features. The clinical examination by the physician is important for classifying prediabetes, either as IGT or IFG.