Glucose volume of distribution affects insulin sensitivity measured by intravenous glucose tolerance test

Abstract

AbstractAimTo determine whether glucose volume of distribution (VdGLUCOSE) affects the diagnosis of impaired insulin sensitivity (IS) when using an intravenous glucose tolerance test (IVGTT).MethodsIndividuals with distinct levels of IS underwent IVGTT after an overnight fast. The prediabetic group (Prediab; n = 33) differed from the healthy group (Healthy; n = 14) in their larger glycosylated hemoglobin (HbA1c of 5.9 ± 0.3 vs. 5.4 ± 0.1%; 41 ± 4 vs. 36 ± 1 mmol/mol; p < 0.001), percent body fat (37 ± 6 vs. 24 ± 3%; p < 0.001) and cardiovascular fitness level (VO2MAX 22 ± 5 vs. 44 ± 5 mL of O2·kg−1·min−1; p < 0.001). Ten minutes after intravenous infusion of the glucose bolus (i.e., 35 g in a 30% solution), VdGLUCOSE was assessed from the increases in plasma glucose concentration. IS was calculated during the next 50 min using the slope of glucose disappearance and the insulin time‐response curve.ResultsVdGLUCOSE was higher in Healthy than in Prediab (230 ± 49 vs. 185 ± 21 mL·kg−1; p < 0.001). VdGLUCOSE was a strong predictor of IS (β standardized coefficient 0.362; p = 0.004). VO2MAX was associated with VdGLUCOSE and IS (Pearson r = 0.582 and 0.704, respectively; p < 0.001). However, body fat was inversely associated with VdGLUCOSE and IS (r = −0.548 and −0.555, respectively; p < 0.001).ConclusionsSince fat mass is inversely related to VdGLUCOSE and in turn, VdGLUCOSE affects the calculations of IS, the IV glucose bolus dose should be calculated based on fat‐free mass rather than body weight for a more accurate diagnosis of impaired IS.