Reproducibility of the Glucagon Test

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Abstract
The influence of the fasting blood glucose (FBG) concentration on the ß‐cell responsiveness to glucagon was studied twice in 9 insulin‐dependent diabetic patients with residual ß‐cell function. At a FBG of 7.7±0.3 mmol/l (mean ±SEM) all patients displayed a preserved ß‐cell function with a plasma C‐peptide concentration of 0.25±0.03 nmol/l 6 min after an i.v. injection of glucagon. In contrast, at a FBG of 3.2±0.01 mmol/l 4 out of 9 patients would have been classified as not having an endogenous insulin secretion. All the patients had the lowest 6 min C‐peptide concentration 0.06±0.01 nmol/l on the day with the lowest blood glucose concentration. The reproducibility of the glucagon test was assessed by comparing the results from two test days in 12 insulin‐dependent, 9 non‐insulin‐dependent diabetic patients and 6 normal subjects. The 6 min plasma C‐peptide concentration, the peak plasma C‐peptide concentration, and the area under the plasma C‐peptide curves were not different on the two test days in any subgroup. In all diabetic patients and normal subjects, the 6 min plasma C‐peptide concentration (r = 0.93, coefficient of variation (CV) = 0.16), the peak plasma C‐peptide concentration (r = 0.93, CV = 0.16) and the area under the plasma C‐peptide curve (r = 0.94, CV = 0.16) were all significantly correlated. The results show that the prevailing FBG significantly affects the outcome of the glucagon test and confirm its reproductibility.