A comparison of intravenous and oral glucose tolerance tests in the dog

Glucose and insulin levels were measured at various intervals after oral and intravenous administration of glucose to 12 normal adult crossbred dogs. The pre-test diet, starvation period and time of testing were all standardised. The glucose (1 g/kg) was delivered as a 50 per cent solution for the intravenous test and in a constant volume of 50 ml for the oral test. A two way analysis of variance demonstrated significantly greater variability with the oral test. Because of consistency and ease of parameter calculation, it was thought that the intravenous glucose tolerance test would be more accurate for assessing glucose intolerance. An intravenous glucose tolerance test was performed under similar conditions on 12 diabetic dogs and the glucose disappearance constants for the normal and diabetic animals compared for various periods. The disparity between normal and diabetic animals was greatest over the 10 to 60 min period (eight samples). Furthermore, when a three sample (10, 20 and 40 min) subset of this period was used a similar difference was obtained. With either the 10 to 60 min period or the 10, 20, 40 min subset, a glucose disappearance value of 2 or less in a dog indicates glucose intolerance.