Different effect of aldosterone on corrected HCO₃^- across primary aldosteronism subtypes

Primary aldosteronism (PA) causes biochemical abnormalities such as hypokalemia and metabolic alkalosis. This study aimed to compare the effects of aldosterone on serum potassium and corrected bicarbonate (cHCO₃^-, defined as Na - Cl - 12) between PA and non-PA and between unilateral and bilateral PA (uPA and bPA, respectively). A total of 463 patients from the Japan Primary Aldosteronism Study II, who had been enrolled as of January 2024, were analyzed. Correlations between plasma aldosterone concentration (PAC) and serum potassium, as well as cHCO₃^-, were evaluated in PA vs. non-PA and in uPA vs. bPA. In the PA group, PAC was significantly correlated with both serum potassium (r = -0.449, P < 0.05) and cHCO₃^- (r = 0.439, P < 0.05), whereas no significant correlations were observed in the non-PA group. Among PA subtypes, uPA showed significant correlations between PAC and serum potassium (r = -0.299, P < 0.05) and cHCO₃^- (r = 0.420, P < 0.05). Conversely, in bPA, PAC showed a weaker correlation with serum potassium (r = -0.178, P < 0.05) and no significant correlation with cHCO₃^-. Even in the analysis with matched PAC between uPA and bPA, a significant correlation between PAC and cHCO₃^- was observed only in uPA (r = 0.415, P < 0.05), whereas no such correlation was found in bPA, with a significant difference between the two groups (P < 0.05). uPA was observed in 96.7% of patients with PA who had PAC ≥ 150 pg/mL and cHCO₃^- ≥ 28 mmol/L. In conclusion, PAC is significantly correlated with cHCO₃^- in uPA, but not in non-PA or bPA. cHCO₃^- is potentially useful for evaluating disease activity in uPA and detecting uPA.