Endocrine Abstracts

We present two cases where, without measurement of cortisol binding globulin (CBG), interpretation of their 250mcg short synacthen test (SST) would have falsely suggested inadequate pituitary-adrenal reserve.

A 62yr old woman was referred with an incidental finding of a pituitary adenoma. Pituitary function tests confirmed gonadotrophin and growth hormone deficiency. Initial and subsequent SSTs were normal (30min cortisol reater than 600nmol/L). Follow up MRI showed spontaneous shrinkage of the adenoma and she underwent a further SST. This showed an inadequate response (0min 253nmol/L, 30min 340nmol/L) despite no clinical suggestion of adrenal insufficiency. At this time she was diagnosed with nephrotic syndrome (serum albumin 19g/L, RR 34-48g/L, urinary protein-creatinine index greater than 3000). We measured CBG; 0 min 23mg/L, 30min 16mg/L (RR 37-48mg/L). The total cortisol to CBG ratio at 30min post-Synacthen was normal at 21 (normal greater than 12). We have not instigated steroid replacement and she remains well.

A 57yr old woman, with hypothyroidism and hypoparathyroidism following thyroidectomy for Graves' disease, had investigations for weight loss. Although adrenal cortex antibodies were positive she had a normal response to 250mcg Synacthen. Repeated SSTs were normal as were plasma renin-activity, aldosterone and ACTH. She subsequently developed acute pancreatitis necessitating ITU. A SST showed a cortisol of 208nmol/L rising to 246nmol/L and she was commenced on hydrocortisone. CBG was low (0min 20mg/L and 30min 18mg/L) with the 30 minute total cortisol to CBG ratio normal at 14. We are currently reducing her steroids as an outpatient, with a view to stopping them. She remains well with no symptoms or signs of adrenal insufficiency.

These cases highlight the potential pitfalls in interpretation of short synacthen tests when only total cortisol is measured. In cases where low CBG is suspected the cortisol/CBG ratio should be measured.