Simple empirical assessment of Beta-cell function by a constant infusion of glucose test in normal and Type 2 (non-insulin-dependent) diabetic subjects

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Abstract
The plasma insulin or C-peptide response to a 90-min constant glucose infusion 5 mg · kg ideal body weight−1·min−1 provides Beta-cell assessment comparable to more intensive methods. In 14 diet-treated Type 2 (non-insulin-dependent) diabetic subjects and 12 non-diabetic subjects, plasma insulin and C-peptide concentrations gave near linear plots against simultaneous glucose values. The ‘glucose-insulin and glucose-C-peptide vectors’ (G-I and G-C vectors), could be extrapolated to predict insulin and C-peptide levels during a 12 mmol/l hyperglycaemic clamp. Predicted concentrations correlated with clamp concentrations, r = 0.94 and r = 0.98 respectively, pr = 0.95 and 0.93 for insulin and C-peptide, respectively. G-I vector slopes in 21 diet-treated Type 2 diabetic subjects with fasting glucose (mean +1 SD) 7.5±2,3 mmol/1, were lower than in 28 non-diabetic subjects, (geometric mean, 1 SD range, 8.4 pmol/mmol (3.3–21.0) and 25.1 pmol/mmol (14.3–44.1), pr = 0.54 ppr = −0.66, pr = −0.57, p p<0.001, respectively). The insulin or C-peptide response to the glucose infusion provides a direct empirical measure of the Beta-cell function, which can be interpreted in relation to obesity or to insulin resistance to assess underlying pancreatic responsiveness.