Should the duration of the insulin tolerance test be shortened to 90 minutes?

The insulin tolerance test (ITT) is a standard growth hormone (GH) provocative test to distinguish children with normal variant short stature (NVSS) from those with GH deficiency (GHD). We reviewed ITTs retrospectively in 52 short children using peak GH concentration of 7 ng/ ml as a cut-off level for GHD (peak GH <7 ng/ ml) and NVSS (peak GH > or =7 ng/ml). The average insulin dosage was 0.1 U/kg in children with NVSS and 0.08 U/kg in GHD. Hypoglycemia was achieved in all cases with an average plasma glucose nadir of 1.8 mmol/l (32 mg/dl) occurring between 15 and 45 min following administration. The average peak GH concentration was 12 ng/ml, occurring at 30-90 min. There were no serious adverse effects from the ITT. We conclude that the appropriate duration of ITT should be 90 minutes. The appropriate timing to obtain samples for plasma glucose level is at 0, 15, 30, 45, 60, and 90 min, and for GH concentrations at 0, 30, 45, 60, and 90 min. The shortened duration of ITT to 90 min will reduce the time spent and also the financial cost for unnecessary samples, while still ensuring a correct diagnosis for the patients.