The ARR is a screening test for primary hyperaldosteronism and Endocrine team input is recommended before undertaking this test. A morning sample is preferred, and the patient should be seated for 15 minutes prior to venepuncture. The patient should have unrestricted dietary salt intake. Various anti-hypertensive medications effect renin and aldosterone measurement therefore medications should be noted. Some medications may need to be discontinued for at least 4 weeks, if possible (in particular spironolactone, eplerenone, amiloride, triamterene and potassium-wasting diuretics).