Insulin requirement in non-insulin-dependent diabetes mellitus: relation to simple tests of islet B-cell function and insulin sensitivity.

Evaluation of simple tests of islet B-cell function and insulin sensitivity as predictors of metabolic control was performed during 3 months of insulin withdrawal in 25 insulin-treated diabetic subjects. All patients had a glucagon stimulated plasma C-peptide concentration above 0.33 nmol/l and a fasting plasma C-peptide concentration above 0.20 nmol/l a few days before insulin withdrawal. Insulin sensitivity was measured as the glucose disappearance rate (k) during an intravenous insulin tolerance test. Two patients were considered insulin-requiring due to high fasting blood glucose levels (greater than 20 mmol/l) and two patients due to an increase in glycosylated haemoglobin of more than 1.1% (greater than approximately 3SD) in combination with weight loss. None of the remaining patients had a significant increase in glycosylated haemoglobin. An inverse correlation was found between stimulated C-peptide levels and insulin sensitivity (r = 0.41, p less than 0.05). Fasting and stimulated C-peptide concentrations of 0.40 and 0.70 nmol/l, respectively, separated non-insulin-requiring patients from a group consisting of both insulin- and non-insulin-requiring patients. At these C-peptide levels the predictive value of a positive test was 100% while the predictive value of a negative test was as low as 33% or 27% depending on whether fasting or stimulated C-peptide concentration was used. Including the k value in the prediction only increased the predictive values of negative tests to 40% and 33%, respectively.