Elevation of the renal threshold for glucose is associated with insulin resistance and higher glycated hemoglobin levels

AIMS/INTRODUCTION: The renal threshold for glucose (RTg) corresponds to a blood glucose of ~180 mg/dL, but in hospitals patients are often encountered who are hyperglycemic but urine glucose test-strip negative, who remain negative for urine glucose even at blood glucose concentrations > 180 mg/dL, implying a high RTg value. In this study, we aimed to identify factors determining high RTg in Japanese patients with type 2 diabetes mellitus (T2DM). MATERIALS AND METHODS: We estimated RTg using urinalysis data from 67 T2DM patients in whom glucose infusion rate (GIR) was determined by hyperinsulinemic-euglycemic clamp. After allocating patients to two groups according to their baseline eRTg (< or ≥ 180 mg/dL), we identified the factors affecting eRTg using simple and multiple linear regression analyses. RESULTS: GIR, glycated hemoglobin A1c (HbA1c), insulin use, and dyslipidemia differed significantly between the groups. In simple regression analysis, GIR, HbA1c, body muscle-to-fat ratio, and insulin use were significantly correlated with eRTg, and in multiple regression analysis, GIR and HbA1c remained independent negative and positive determinants, respectively, with the contribution of GIR being substantial. In receiver-operating characteristic (ROC) curve analysis, when GIR < 5.7 was used as the insulin resistance threshold, the cut-off value of eRTg was 189 mg/dL (P = 0.0001). Furthermore, in ROC analysis using eRTg ≥ 189 mg/dL, the cut-off value for HbA1c was 8.0% (P = 0.0006). CONCLUSIONS: High eRTg is associated with low GIR and high HbA1c, with GIR making a substantial contribution.