Discordance in the levels of hemoglobin A1C and glycated albumin: Calculation of the glycation gap based on glycated albumin level

Objective The glycation gap (G-gap) is an empirical measure of the extent of the difference between HbA1C and fructosamine levels. Several studies have shown that the presence of a G-gap is linked to diabetic nephropathy, but possible artifacts caused by dependence of the fructosamine level on the extent of serum protein metabolism require careful consideration. We investigated the consistency of G-gaps measured by assaying glycated albumin (GA) levels to identify factors associated with G-gap variations. Method A total of 457 pairs of observations, like an HbA1c and GA measurement at the same clinic visit, were obtained from 170 Korean patients with type 2 diabetes. HbA1c and GA levels were measured simultaneously in two or three separate occasions. Each G-gap was calculated as the difference between the measured HbA1c level and that predicted by the GA level. All patients underwent abdominal computed tomography, and the areas of subcutaneous and visceral fat were measured. Results The G-gaps were all significantly inter-correlated over time (γ = 0.755, P < 0.001).The direction of each G-gap was consistent. The body mass index (BMI), visceral fat area, and the estimated glomerular filtration rate (eGFR) increased linearly from the lowest to the highest G-gap quartile (all P values < 0.05). Upon multivariate analysis, both visceral fat area and the eGFR were significantly associated with a G-gap. Conclusions A G-gap determined using GA measurements is consistent within an individual over time. The G-gap is associated with visceral fat and kidney function in patients with type 2 diabetes.