Test Background Cortisol is the major glucocorticoid. Synthesis and secretion are stimulated by ACTH and are subject to a diurnal rhythm, with peak values occurring in the early morning. Excess cortisol occurs in Cushing’s syndrome; causes include: hypersecretion of ACTH, adrenal hyperplasia or neoplasia, and exogenous corticosteroid administration. Common causes of decreased cortisol synthesis include CAH, autoimmune and iatrogenic-mediated adrenal destruction, amyloidosis, hypopituitarism and occasionally sepsis. Dynamic function tests, eg. synacthen stimulation tests or dexamethasone suppression tests, may be used in the differential diagnosis of hypo- and hyper-secretion respectively.
Clinical Indications Inadequate cortisol levels/Addison’s disease: weight loss, muscle weakness, fatigue, low blood pressure or abdominal pain. Stress can induce an adrenal crisis that requires immediate medical attention (Addisonian crisis)
Cushing’s syndromes: hypertension, hyperglycaemia, obesity, fragile skin, hyperpigmentation, muscle weakness and osteoporosis
Presentation of irregular menses (women) or delayed development/short stature (children)