Statistical analysis of the reproducibility of the intravenous glucose tolerance test and the serum insulin response to this test in the middle-aged men

The reproducibility of the intravenous glucose tolerance test (IVGTT) and the serum insulin response to this test have been studied in 48 healthy middle-aged men participating in a health screening program. Two tests were done 4-6 weeks apart. The subjects were ambulatory, and no diet prescriptions other than recommendation of an overnight fast were given. Under these circumstances the correlation between the K values of the two tests was low (r equals 0.55), and the equation for linear regression was y equals 0.56 x + 0.61. The intraindividual variation was 21 per cent, expressed as the coefficient of variation. The early increases in glucose-stimulated serum insulin concentrations in the two tests were significantly correlated (r equals 0.87), and this equation for linear regress was y equals 0.81 x + 10. The coefficient of variation intraindividually for this determination was 20 per cent. We conclude that the K values of the IVGTTs must be judged with caution when obtained in ambulatory practice, especially when the result is used for preventive measures and long-term follow-up of asymptomatic individuals.