Endocrine Abstracts

The Insulin tolerance test (ITT) is regarded as the gold-standard for diagnosing ACTH deficiency but some normal subjects do not exhibit an adequate cortisol response to hypoglycaemia. Identification of false fail cases in pituitary patients is important so as to avoid unnecessary treatment with glucocorticoids. Two hundred consecutive ITTs in pituitary patients were analysed. Twenty six (13 males) failed the ITT and subsequently have a Short Synacthen test (SST). 20 patients were deemed to have a low likelihood of ACTH deficiency (basal am cortisol > 200 nmol/l or peak cortisol response to ITT > 400 nmol/l, or otherwise normal remaining pituitary axes). Using modern cortisol immunoassays, a cut-off of 450 nmol/l was regarded as a normal response to both ITT and SST. 17/26 patients (65.3%) failed the ITT but passed the SST. The positive predictive value (PPV) for passing the SST when the patient had an am cortisol of > 200 nmol/l or a peak cortisol response to ITT of > 400 nmol/l was 70% (95% CI 58–80%) and 77% (95% CI 55–91%) respectively. Patients with a normal SST were taken off hydrocortisone and none developed an adrenal crisis or convincing hypoadrenal symptoms (median follow-up 27 months, IQR 5–37). A high percentage of patients who fail the ITT but have an am cortisol of > 200 nmol/l or peak response to hypoglycaemia of > 400 nmol/l will pass the SST. These patients should be retested using the SST before committing them to life-long treatment with glucocorticoids.