Glycosylated hemoglobin and fructosamines: Does their determination really reflect the glycemic control in diabetic patients?

The present experiment was designed to determine whether scavenging capacity of serum, in addition to glucose level, influences hemoglobin and serum protein glycosylation in non-insulin dependent diabetic patients. For this purpose forty-seven patients homogeneous for age, disease duration, therapy and glyco-metabolic control were selected. Fasting and post-prandial glycemia and insulinemia as well as glycosuria were weekly analysed during the sixty days preceding glycosylated hemoglobin (HbA1c), fructosamines and serum scavenging capacity determination. This last parameter has been evaluated by a method based on the property of β-phycoerythrin (β-PE) to loss its fluorescence when damaged by oxygen radicals, that were produced by Cu⁺⁺ and H₂O₂. The oxygen radical absorbance capacity (ORAC(OH)) of serum was assayed as the ability of serum to delay the loss of β-PE fluorescence. As expected, a statistically significant positive correlation was found comparing both fructosamines and HbA1c levels with mean fasting glycemia measured over twenty and sixty days, respectively. The key result of this study is represented by the finding that both HbA1c and fructosamines levels show a statistically significant negative correlation with ORAC(OH) values. This correlation can explain a large percent of the data dispersion occurring when ORAC(OH) is not taken into account. In order to better describe the role of ORAC(OH), patients were separated into two sub-groups with an ORAC(OH) lower (L-ORAC(OH)) and greater (H-ORAC(OH)) than 100 U/ml. Examining the correlation between mean fasting glycemia and the two glycosylated proteins considered in these two sub-groups, curves with different slopes were obtained, supporting that the rate of glycosylation of both proteins was higher in L-ORAC(OH) patients as compared to those with H-ORAC(OH). Present data suggest that for a proper interpretation of the HbA1c and fructosamines data in diabetic patients, the scavenging capacity level of serum should be taken into account.