Measurement of both Free Cortisol and Cortisone are useful in diagnosing patients with low-renin hypertension caused by apparent mineralocorticoid excess.
Cortisol is a steroid hormone and helps regulate metabolism, reduce inflammation and control blood sugar levels and is produced by the adrenal glands. It rises in response to stress, but it will also rise in those taking steroids (even as creams or asthma inhalers) and briefly after eating. Persistently raised cortisol levels may indicate underlying Cushing's disease. Too little cortisol may indicate adrenal deficiency and Addison’s disease. Cortisol levels naturally deplete throughout the day so a 9am sample is best.