Aldosterone is the main sodium-retaining hormone produced by the adrenal glands. It increases the reabsorption of sodium and water along with the excretion of potassium in the distal tubules of the kidneys. This action raises blood pressure. Approximately 1-2% of individuals with primary hypertension have primary hyperaldosteronism characterized by hypokalemia (low potassium) and low direct renin. Because serum aldosterone concentrations vary due to dietary sodium intake and body positions, some physicians prefer measurement of 24-hour urine concentrations for aldosterone. The upright value (obtained after 2 hours of upright posture) should be about 2 to 5 times the supine value obtained from recumbent patient in early am before arising from bed.