Depth and duration of hypoglycaemia achieved during the insulin tolerance test

Context: The insulin tolerance test (ITT) is the gold standard for assessment of the pituitaryadrenal axis but its use is limited because of concerns relating to the risk of hypoglycaemia. Objective: This study examined the depth and duration of hypoglycaemia achieved during the test in a large cohort of patients. Design: Two hundred and twenty ITTs were performed from 2005 to 2010. Setting: A 1200-bed University Teaching Hospital. Patients: Two hundred and twenty ITTs were carried out in patients with suspected or known pituitary disorders. Interventions: Intravenous insulin was administered to achieve nadir plasma glucose (NPG) of 2.2 mmol/l (39.6 mg/dl). Blood chemistry to show the cortisol and GH response to hypoglycaemic stress was measured. Main outcome measures: Predictors of depth and duration of hypoglycaemia, adverse events and within-subject variability of nadir glucose, peak cortisol and peak GH were studied. Results: Thirty percent of the cohort achieved a nadir glucose of !2.0 mmol/l (36 mg/dl) that lasted for 60 min or more. The NPG correlated positively with fasting plasma glucose (FPG; rZ0:56; P!0.0005), insulin dose (rZ0.27; P!0.0005) and weight (rZ0.21; P!0.004). The within subject variability of nadir glucose was 15.2%, peak cortisol was 11.7% and peak GH was 6.4%. The factors determining nadir blood glucose were FPG (bZ0.56, P!0.0005, 20% contribution) and weight (bZ0.14, P!0.05, 2% contribution). The five patients with adverse events had NPG and insulin dose comparable with the rest of the population. Conclusions: The hypoglycaemia achieved during the ITT is much lower than the target required. However, adverse events are few and do not relate to the depth of hypoglycaemia.