GLYCOHEMOGLOBIN (HbA1), 20 tests

BASIS OF THE TEST

In healthy individuals, glucose circulates in the blood. Red blood cells are highly permeable to glucose. The concentration of glucose in red blood cells and plasma is approximately the same. The amount of glucose in the red blood cells increases proportionately as plasma glucose levels increase. Glucose may react with the haemoglobin molecules of red blood cells to form glycohaemoglobin. This reaction depends entirely on the concentration of glucose in the red blood cell and consists of two stages: one which is quick and reversible in which aldimines are formed, and a slow and relatively irreversible stage in which stable glycohaemoglobin (ketoamine) is formed, which will last throughout the useful life span of the red blood cell (approximately 120 days). In this ion exchange resin method (batch technique), the first step is to haemolyse the whole blood with the lysing reagent. The next step is to mix the lysed blood with the resin. At a certain pH value and conductivity, the fraction of non-glycated haemoglobin (HbA0) binds to the resin, while the HbA1 fraction remains free in the supernatant. Separation by centrifugation of both stages (resin and supernatant) enables the evaluation of the relative proportion of the HbA1 fraction in relation to the total haemoglobin which is measured separately. The results are calculated by comparing them with a standard or control of a known concentration.

PRINCIPLE

At a certain pH value, the HbA0 hemoglobin fraction is retained by the ion exchange resin, while the HbA1 fraction (glycosated hemoglobin) has a net charge that will make it to remain in the supernatant. The rapid phase separation of resin from the supernatant by centrifugation, will allow a quick evaluation about the relative proportion of HbA1 with regard to the total hemoglobin (Batch technique).