CLINICAL STUDY An audit of the insulin-tolerance test in 255 patients with pituitary disease

Objective: The insulin-tolerance test (ITT) is currently considered to be the gold standard for evalu-ating adults suspected of GH deficiency (GHD). The aim of this study was to determine factors that may influence nadir blood glucose (BG) when using a mean insulin dose of 0.1 IU/kg body weight. Furthermore, we wanted to evaluate the safety and GH-related aspects of the ITT. Design: ITT was performed in 277 patients, of whom 255 (129 females) were eligible for evaluation. Results: Multiple regression analysis, including the whole population, showed that the major deter-mining factors for nadir BG were basal BG and body mass index (BMI) \u85 P, 0:02: No serious adverse event was recorded. Sixty-three percent of all patients tested had severe GHD with peak GH response to hypoglycaemia below 7.8 mIU/l. The positive predictive value for IGF-I was 0.82 and the negative predictive value was 0.47, using a cut-off value corresponding to 22 S.D. GH peak response to hypo-glycaemia decreased with increasing numbers of other pituitary hormone deficiencies. Conclusions: When determining the dose of insulin based on weight, factors like pre-test BG and BMI should also be considered. We propose an algorithm stating that the dose of insulin should be 0.1 IU insulin/kg body weight minus 2 IU if pre-test BG is,4.0 mmol/l and minus 2 IU if BMI is,20 kg/m2 in order to take these factors into account. Our findings furthermore support the concept that the low-dose ITT is a safe test in adults, when performed in experienced hands. It was confirmed that IGF-I is not sufficient when diagnosing GHD in adults, and reliable stimulation tests like ITT are required in the diagnosis. European Journal of Endocrinology 147 41–4