Safety of insulin tolerance test for the assessment of growth hormone deficiency in children

Objective: To determine the safety of insulin tolerance test (ITT) for assessing growth hormone (GH) deficiency in children. Methods: This hospital based study was conducted at the National Institute of Child Health, Karachi from 1st November 2008 till 30th October 2009. All children suspected of growth hormone deficiency, were included after excluding all other causes of short stature. Verbal informed consent was taken from the parents. Children less than 2 years of age, weighing less than 10 kg, untreated/inadequately treated hypothyroidism or Addison's disease, epilepsy, having history of hypoglycaemic fits or cardiac disease were excluded. All children were subjected to the international standard protocol of ITT and their samples of growth hormone and blood sugars were drawn. Complications during the procedure like hypoglycaemia, hypothermia, loss of consciousness, fits, vomiting and failure to achieve hypoglycaemia were recorded. Insulin tolerance test was performed on a total of 168 subjects. The data was entered in SPSS version 17 for analysis. Results: A total of 168 children were subjected to the ITT. Four of them were abandoned as they could not achieve hypoglycaemia despite repeating the dose of insulin. Results were analyzed on 164 children whose mean age was 10 +/- 3.5 years. There were 96 (58%) males and 68(41%) females. Over all 79.8% children achieved hypoglycaemia. None of the subjects developed any complication (fits, loss of consciousness,) or required intravenous glucose during the test and it was completed in all children with close monitoring. The results showed that there was a significant effect of time after insulin administration on both the blood glucose level (BG) and growth hormone (GH) levels. The blood glucose level decreased rapidly after administration of insulin and was lowest 30 minutes after injection and showed an increasing trend in subsequent readings, becoming almost equal to the baseline value 120 min after injection. From the study group 111 (66%) children were diagnosed as having growth hormone deficiency, 52 (31.3%) were normal and 1(0.6%) had growth hormone insensitivity. Conclusion: ITT in children was found to be a safe and reliable test but can be potentially dangerous and requires very close monitoring and supervision and should be performed in a center with experienced staff.