Spot urine potassium as a potential screening test for aldosterone breakthrough

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.

This was a cross sectional study involving 94 patients who were on an ACEI or ARB for a minimum duration of 40 weeks. An aldosterone cut off value of 102 pg/ml was used to define aldosterone breakthrough based on a previous study. Patients with primary hyperaldosteronism, conditions giving rise to secondary hyperaldosteronism and those who were on drugs which could interfere with the renin-angiotensin-aldosterone system were excluded. The study patients had their blood sample analysed for renal profile, renin, aldosterone and urine sample analysed for urine potassium.

Incidence of aldosterone breakthrough in this study was 23.4%. The median urine potassium was 62.0 mmol/L in the aldosterone breakthrough group compared to the non-breakthrough group which was 38.5 mmol/L. The urine potassium showed statistically significant difference between both groups (p=0.016). The correlation coefficient was 0.284; statistically significant (p=0.006) as the sample size was large (n=94).

A raised urinary potassium after initiating treatment ith ACEI or ARB is a potential screening test for aldosterone breakthrough.