Hemoglobin A1 and serum fructosamine levels in hyperthyroidism.

The severity, prevalence and pathogenesis of abnormalities of carbohydrate metabolism in hyperthyroidism are incompletely defined. The extent of glycosylation of proteins provides an objective, retrospective index of glycemic control. We have measured the percent hemoglobin A1, random plasma glucose level and serum concentrations of fructosamine, total protein and albumin in hyperthyroid and euthyroid subjects attending a hospital-based thyroid clinic. A significant (p = 0.002) increase in the mean value for hemoglobin A1 and a significant (p = 0.0003) decrease in the mean values for fructosamine were found in the hyperthyroid group. The lower mean fructosamine value in the hyperthyroid group was attributed to a concomitant decline in the mean albumin concentration (p = 0.001). The mean value for glucose tended to be higher in the hyperthyroid group, but the difference did not reach significance at the 0.05 level (p = 0.09). The finding of a higher mean hemoglobin A1 concentration in hyperthyroid patients compared to euthyroid subjects is new evidence for a persistent abnormality in glycemic regulation in most thyrotoxic patients.