Feasibility and Outcomes of a Modified Intravenous Glucose Tolerance Test: Implications for Glucose Clearance Rate in Euglycemic Black Adults

Introduction: The intravenous glucose tolerance test (IVGTT) is acknowledged as the gold standard for assessing insulin sensitivity, as it provides the glucose clearance rate (Kg) from the bloodstream. The ICARUS panel expert protocol for the implementation of the IVGTT involves the administration of a high dose of glucose over a brief bolus period, which is risky and may result in discomfort. This study aimed to demonstrate the feasibility of a heparin-assisted IVGTT with a lower glucose infusion rate and to determine the glucose clearance rate from blood (Kg) for healthy black African adults using a modified ICARUS protocol. Methods: In a modified ICARUS protocol, heparin was administered to six healthy black African volunteers to prevent clotting in an indwelling catheter. Then, an infusion of 0.33 g/kg glucose was administered over 5–10 min instead of the usual 0.50 g/kg over 3 min. Blood sampling was performed every 5–10 min for up to 95 min. Blood glucose levels were determined using the glucose oxidase method. Timed blood glucose curves were plotted, and the following parameters were determined: area under the curve (AUC), baseline return time, and glucose clearance rate (Kg). Results: No bleeding symptoms or other adverse events were observed. The blood glucose peak ranged from 9.4 to 15.3 mmol/L. The baseline returned time ranged from 45 to 55 minutes. Kg ranged from 1.6 to 2.7, depending on the amount of infused glucose. The AUC varied with the amount of infused glucose and infusion duration. The Staub effect was not observed in this study. The features of the curves were all plausible compared to those obtained in healthy subjects using the original Icarus protocol. Conclusion: Under our experimental conditions, we achieved IVGTT using a heparin-assisted IVGTT protocol with reduced glucose infusion rates, and determined the glucose clearance rate. This protocol is feasible and can potentially be used to assess insulin sensitivity. The protocol can be applied on a larger scale to determine its statistical features.