Endocrine Abstracts

Introduction: The insulin stress test (IST) used to assess the hypothalamic–pituitary–adrenal (HPA) and growth hormone axes requires blood glucose to fall below 2.5 mmol/l. This level of hypoglycaemia is considered safe for selected patients but blood glucose levels below this are associated with increasing risk. We reviewed the depth and length of hypoglycaemia in a cohort of patients undergoing IST.

Method: Between October 2004 and 2008, 138 IST were performed. Medical notes were reviewed for 121 cases. Reasons for the IST, insulin dose, blood glucose and cortisol response was noted. Adverse outcomes were examined.

Results: IST was performed following hypophysectomy (24), cranial irradiation (15), pituitary adenoma (48), hormone deficiency (32), to assess growth hormone production (2). Standard actrapid dose (0.15 iu/kg) was given to 101 cases, resistant dose (0.3 iu/kg) to 17 cases and sensitive dose (0.1 iu/kg) to three cases. The mean nadir blood glucose was 1.5 mmol/l (range 0.3–3.4). All but eight cases achieved blood glucose < 2.5 mmol/l (1of whom had an insufficient cortisol response necessitating repeat testing). The majority of cases (73) remained hypoglycaemic (< 3.5 mmol/l) for 90 min. Thirty seven were hypoglycaemic for 60 min and 11 for 30 min. Nine patients were given rescue treatment prior to the end of the test. Sufficient cortisol response was seen in 81 cases. There were five adverse outcomes. One case underwent emergency coronary artery bypass. The remainder suffered loss of consciousness with three possible fits.

Summary: Many patients suffered severe, prolonged hypoglycaemia beyond that required to perform the assessment. Significant adverse events were suffered by 4%.

Conclusion: Significant hypoglycaemia is unpleasant and may be harmful. Current protocols developed in the 1970 s frequently result in severe prolonged hypoglycaemia. The use of bedside testing of whole blood glucose combined with an insulin/dextrose infusion should allow a satisfactory test without uncontrolled levels of hypoglycaemia.