The insulin tolerance test (ITT) is the gold standard for assessing growth hormone (GH) and cortisol production in pituitary disease, However it is potentially hazardous, requires medical supervision and adequate hypoglycemia may not be achieved. We retrospectively examined the records of 185 consecutive patients aged 14-76 years with pituitary disease who underwent the ITT over 18 months. Testing was performed in the endocrine day ward by an experienced endocrine nurse. Absolute contraindications were seizure disorders, heart disease and abnormal ECG.
The standard insulin dose was 0.15 unit/Kilogram. Acromegalic and diabetic patients received 0.2unit/Kilogram and patients with basal cortisol less than 100 nanomole/ litre received 0.1 unit/kilogram of insulin. Adequate hypoglycemia (nadir glucose less than 2.2 millimole/litre) was achieved in 89%. 20 patients failed to achieve adequate hypoglycemia; 12 had acromegaly, 3 diabetes and 2 were obese (Body mass index > 30 kilogram/ metre square). Most patients (84 %) achieved nadir glucose at 15-30 minutes. 16 patients had basal cortisol < 100 nanomole/litre. The majority of patients achieved peak cortisol and GH between 45 and 90 minutes (70% and 72% respectively). Late cortisol and GH peak responses ( between 90-120 minutes) were seen 17% and 3% of patients respectively. One patient required intravenous dextrose for impaired consciousness. There were no other serious adverse events.
In specialised units with adequate expertise, the ITT is a safe test even in elderly patients and those with hypocortisolemia. The standard 90 minute cut-off for the ITT misses one in six peak cortisol responses.
22 - 24 Mar 2004
British Endocrine Societies