Determining the physiologic effects of aldosterone on sodium-potassium exchange in the renal tubule is as simple and accurate as measuring aldosterone excretion and plasma renin activity. We compared the 24-hour urinary potassium clearance before and after three days of oral administration of spironolactone while the patient was on a high salt diet. Greater than 50% reduction in potassium clearance after administration of spironolactone indicates pathologic secretion, which suggests the need for exploration of the adrenals after exclusion of secondary aldosteronism.
Birchall R, Batson HM. Test for Pathologic Secretion of Aldosterone. JAMA. 1968;206(9):2114-2117. doi:10.1001/jama.1968.03150090190034