Plasma renin, aldosterone, cortisol, and adrenocorticotropic hormone (ACTH) should be measured in evaluation of all of the following: Primary and secondary adrenal insufficiency Primary hyperaldosteronism and secondary hyperaldosteronism Refractory hypertension The plasma aldosterone / renin ratio calculated from measurements obtained with the patient in an upright posture is the best screening test for hyperaldosteronism, provided that plasma renin activity is < 0.5 ng / mL / h (< 0.5 mcg / L / h) and aldosterone is > 12 to 15 ng / dL (333 to 416 pmol/L).