Comparable application of the OCT and Abbe refractometers for measurements of glycated hemoglobin portion in blood

It is known that glucose interacts with plasma proteins and hemoglobin in erythrocytes. Glycated (glycosylated) hemoglobin is the result of an irreversible non-enzymatic fixation of glucose on the beta chain of hemoglobin A. The amount of glycated hemoglobin depends on blood glucose concentration and reflects the mean glycemia of about the previous 2-3 months. Glycated hemoglobin is a useful marker for long-term glucose control in diabetic patients. Therefore, the search of quick and high sensitive methods for measurement of glycated hemoglobin portion in blood is important. This study is focused on the determination of refractive index of hemoglobin solution at different glucose concentrations. Measurements were performed using Abbe refractometer at 589 nm and optical coherence tomography (OCT) at 820 nm. The different amount of glucose (from 0 to 1000 mg/dl with a step 100 mg/dl) was added to hemoglobin solution. Theoretical values of refractive index of hemoglobin solutions with glucose were calculated supposing non-interacting hemoglobin and glucose molecules. There is a difference between measured and calculated values of refractive index. This difference is due to glucose binding to hemoglobin. It is shown that the refractive index measurements can be applied for the evaluation of glycated hemoglobin amount.