Basal morning serum cortisol for the assessment of hypothalamic, pituitary adrenal axis function

Background: The study of hypothalamic, pituitary adrenal axis function requires complex tests. However, the measurement of basal morning serum cortisol levels may be a simple measure to evaluate this axis. Aim: To determine if an isolated morning measurement of basal serum cortisol levels in the absence of stress, may predict the indemnity of the hypothalamic, pituitary adrenal axis. Material and methods: Morning cortisol levels in the basal period and 30 minutes after the injection of 50 μg ACTH were measured in 76 patients with a mean age of 52 years (48 females), operated of a pituitary tumor, without Cushing syndrome and not using steroids or oral estrogens. Twenty healthy volunteers with a mean age of 30 years (11 males) were studied as controls. In this last group, the lower limit of normal stimulated cortisol levels was defined as the mean value less two standard deviations and corresponded to 17 μg/dl. Results: Based on stimulated cortisol levels, 15% of operated patients had a hypothalamic, pituitary adrenal axis dysfunction. Using cut-off levels of less than 5, 7.5 and 10 ug/dl, basal cortisol levels had a sensitivity for the diagnosis of hypothalamic, pituitary adrenal axis dysfunction of 64, 81 and 100%, respectively. The figures were 100, 95 and 66% for specificity respectively, 100, 75 and 34% for positive predictive value and 94, 97 and 100% for negative predictive value. Conclusions: A basal morning cortisol value over 10 ug/dl discards the presence of hypothalamic, pituitary adrenal axis dysfunction