Fallibility of the intravenous glucose tolerance test as a measure of endogenous glucose turnover.

We have used hepatectomized, nephrectomized dogs receiving a constant infusion of unlabeled glucose as well as conscious, unrestrained guinea pigs in order to investigate the calculation of basal glucose kinetics from intravenous glucose tolerance tests (IVGTT). In the dogs, we were not able to determine the known rate of appearance (Ra) or disappearance (Rd) of glucose within 50% of the actual value by means of IVGTT. In the guinea pigs, we found that Ra calculated from IVGTT was 250% higher than Ra determined by means of the validated technique of the primed-constant infusion of 6-3H-glucose in tracer quantities. When live Escherichia coli were infused into the guinea pigs, the isotope-tracer technique revealed a 100% increase in Ra yet Ra appeared to be decreased by 80% when calculated by means of IVGTT. We concluded that basal glucose kinetics cannot be determined reliably from IVGTT, and that in certain pathologic conditions the direction of change in Ra and Rd from the basal state may be incorrectly predicted.