Treatment with angiotensin converting enzyme inhibitors (ACEIs) or angiotensin receptor blockers (ARBs) may suppress aldosterone production only in the initial phase of treatment and subsequently lead to a rising level of aldosterone to baseline or higher. This phenomenon is described as aldosterone breakthrough. Apart from serial plasma aldosterone levels, there are no other test to identify this condition. The purpose of this study was to evaluate the role of spot urine potassium as a potential screening test for aldosterone breakthrough.