Isolated hypoaldosteronism is a cause of hypovolemic but not euvolemic hyponatremia

Abstract

INTRODUCTION. Hypoaldosteronism is characterized by hyperkalemia, and/or hypovolemic hyponatremia (HH), often accompanied by metabolic acidosis. HH is typical of hypoaldosteronism, whereas euvolemic hyponatremia (EH) is not. The purpose of the current study is to describe the characteristics of hyponatremia in hypoaldosteronism, and elucidate whether EH can be considered part the disease’s spectrum. METHODS. In a hypoaldosteronism cohort, we analyzed the factors associated with hyponatremia, comparing the characteristics of EH and HH and their associated factors. Correlation analyses of mineralocorticoid biomarkers, such as the transtubular potassium gradient (TTKG), and the urinary Na+/K+ ratio (UNa+/UK+) with serum and urinary electrolytes were performed in both types of hyponatremia. RESULTS. Of 112 hypoaldosteronism episodes, 77.7% were ≥ 65 years old, 44.6% were women and 80 (71.4%) had hyponatremia. Hyponatremia was negatively associated with the presence of chronic kidney disease, and positively with a hypovolemic state, malnutrition, a prior history of hyponatremia and glucocorticoid therapy. HH: 61/80 and EH: 19/80 episodes. HH was associated with an age ≥ 65 years and the use of diuretics, as well as factors related to an aldosterone deficit and/or mineralocorticoid resistance. In HH, but not in EH, urinary potassium was correlated with the TTKG, and urinary sodium with both the TTKG and the UNa+/UK+. CONCLUSION: Both HH and EH can be observed in hypoaldosteronism. However, only the former would be related to insufficient mineralocorticoid activity.