Bioimpedance spectroscopy uncovers extracellular fluid excess in primary aldosteronism

OBJECTIVE: Primary aldosteronism is a common but underdiagnosed cause of secondary hypertension, characterized by volume overload. Bioimpedance spectroscopy is widely used to assess fluid status in dialysis patients. We examined whether this method can distinguish primary aldosteronism from essential hypertension. DESIGN: Patients with confirmed primary aldosteronism (n = 77), essential hypertension (n = 90), and normotensive controls (n = 79) were prospectively recruited for a cross-sectional comparison. METHODS: Total body water, extracellular and intracellular water, and overhydration were measured using bioimpedance spectroscopy. Analyses were adjusted for sex, age, body surface area, estimated glomerular filtration rate, diuretic or spironolactone use, and comorbid diabetes or heart failure. Routine laboratory and hormonal tests were performed. RESULTS: Extracellular water volume was 0.69 ± 1.04 and 0.88 ± 1.04 L/m2 higher, and overhydration 0.76 ± 1.4 and 0.92 ± 1.4 L greater, in primary aldosteronism than in essential hypertension and normotensive controls, respectively (p < 0.001 for all). Total body water did not differ significantly among groups (21.3 ± 2.2, 21.0 ± 2.8, and 21.6 ± 2.4 L/m2, respectively; p = 0.083). Plasma N-terminal pro-atrial natriuretic peptide concentration was highest in primary aldosteronism. Primary aldosteronism severity correlated positively with extracellular water volume (rS = 0.31), overhydration (rS = 0.43), and extracellular-to-intracellular water ratio (rS = 0.36; p < 0.01 for all). CONCLUSION: Extracellular water overload in primary aldosteronism can be assessed using bioimpedance spectroscopy. Further research should determine whether addition of this method to current approaches can improve diagnostic accuracy for primary aldosteronism.