Cut-off values for sufficient cortisol response to low dose Short Synacthen Test after surgery for non-functioning pituitary adenoma.

Abstract

The aim was to study the prevalence of secondary adrenal insufficiency before and after surgery for non-functioning pituitary adenomas, as well as determine risk factors for developing secondary adrenal insufficiency. A secondary aim was to determine adequate p-cortisol response to a 1-μg Short Synacthen Test after surgery. Longitudinal cohort study. One hundred seventeen patients (52/65 females/males, age 59years) undergoing primary surgery for clinically non-functioning pituitary adenomas were included. P-cortisol was measured in morning blood samples. Three months after surgery, a Short Synacthen Test was performed. All tumours were macroadenomas (mean size 26.9mm, range 13-61mm). The surgical indications were visual impairment (93), tumour growth (16), pituitary apoplexy (6) and headache (2). Before surgery, 17% of the patients had secondary adrenal insufficiency (SAI), decreasing to 15% 3months postoperatively. Risk of SAI was increased in patients operated for pituitary apoplexy (p < 0.001), while age, sex, tumour size and complication rate were not different from the remaining cohort. Three months after surgery, all patients with baseline p-cortisol ≥ 172nmol/l (6.2μg/dl) and peak p-cortisol during Short Synacthen Test ≥ 320nmol/l (11.6μg/dl) tapered cortisone unproblematically. In patients with intact hypothalamic-pituitary-adrenal axis, p-cortisol peaked < 500nmol/l (18.1μg/dl) during Short Synacthen Test in 48% of patient. Pituitary surgery is safe and transsphenoidal surgery rarely causes new SAI. Relying solely on morning p-cortisol for diagnosing secondary adrenal insufficiency gives false positives and the Short Synacthen Test remains useful. A peak p-cortisol ≥ 320 during (11.6μg/dl) Short Synacthen Test indicates a sufficient response, while < 309nmol/l (11.2μg/dl) indicates secondary adrenal insufficiency.