Lower Renal Threshold for Glucose Reabsorption in Type 1 Diabetes Mellitus (T1DM) May Explain the Smaller Contribution of SGLT2 Inhibitors to the Improvement of Plasma Glucose Control Compared with T2DM

INTRODUCTION: Previously, we reported that the renal threshold for glucose reabsorption can be measured as the lowest plasma glucose level that correlates with the first detectable appearance of urine glucose. These data revealed significant variations among patients with type 2 diabetes mellitus (T2DM), and there was a significant negative correlation between the renal threshold for glucose reabsorption and HbA1c levels following treatment with the sodium-glucose co-transporter 2 (SGLT2) inhibitor ipragliflozin. Recently approved SGLT inhibitors may not show the same efficacy in patients with T1DM as in those with T2DM unless the renal threshold for glucose reabsorption shows similar levels between the two groups. SGLT2 inhibitors improve plasma glucose control in patients with T2DM by reducing glucose reabsorption via the epithelial cells of the proximal tubule. METHODS: The renal threshold for glucose reabsorption was defined as the minimum blood glucose concentration that results in the presence of measurable glycosuria in at least 12 measurements. RESULTS: The renal threshold for glucose reabsorption in patients with T2DM [n = 64; 201.8 ± 33.6 (range 121–268) mg/dL] was significantly higher than that in patients with T1DM [n = 33; 171.0 ± 33.0 (range 76–259) mg/dL; p = 0.00022]. CONCLUSION: The renal threshold for glucose reabsorption in patients with T1DM was near the normal range and significantly lower than that in patients with T2DM. The efficacy of the SGLT2 inhibitor was better in patients with a higher renal threshold for glucose reabsorption. Thus, these results indicate that it is advisable to estimate the renal threshold for glucose reabsorption prior to initiating SGLT2 inhibitor therapy in patients with T1DM.