Endocrine Abstracts

Introduction: Hypoaldosteronism can be induced by a deficit of aldosterone production (AldDef) or a mineralocorticoid resistance (MinRes). Experts have proposed to use hyperkalemia-based aldosterone values for this purpose. However, there is no a range of aldosterone values indicating one of this type of hypoaldosteronism. In 2008, Adam W. R.¹ hypothesized that the factored aldosterone (FAldo) could be useful differentiating hypoaldosteronism secondary to MinRes from AldDef. We aimed to determine the accuracy of aldosterone and FAldo values classifying hypoaldosteronism cases as AldDef or MinRes.

Methods: Retrospective study of adult cases of isolated hypoaldosteronism. Data from the aldosterone measurement day were analyzed. The presence of mineralocorticoid-resistance factors (ResF) was used to define hypoaldosteronism as MinRes. The absence of ResF defined hypoaldosteronism as AldDef. FAldo is obtained of the formula: blood aldosterone-ng/dl/(blood potassium-mmol/l– 4.2). FAldo value > 10 is suggestive of MinRes. The area under the curve (AUC) of the receiver operator characteristic (ROC) curve was used for determining the accuracy of aldosterone and Faldo values classifying hypoaldosteronism cases as MinRes or AldDef. Aldosterone values were analyzed both indistinctly from the presence of hyperkalemia and only in those with hyperkalemia. FAldo, since is already an aldosterone value corrected by kalemia, was analyzed indistinctly from the presence of hyperkalemia.

Results: 88 hypoaldosteronism cases, age: 74±13 years, 39 (46.4%) were female, 60/88 (68.2%) had MinRes. Mean FAldo values were different between those with and without MinRes (22.7 vs. 7.5 ng/dl/mmol/l, P=0.007). Mean Aldosterone values were also different between these groups (19.2 vs. 7.5 ng/dl, P=0.032). In the entire cohort, the AUC of FAldo for MinRes was 0.721 (95%CI: 0.61-0.83, P=0.003), while AUC of aldosterone values was 0.630 (95%CI: 0.51-0.75. P=0.065). During hyperkalemia, the AUCI of aldosterone values was 0.627 (95%CI: 0.48-0.78. P=0.137). The cut-off point of FAldo>10 had a sensitivity of 62%, a specificity of 81%, a predictive positive value of 90.2% and a predictive negative value of 43.6% to identify MinRes hypoaldosteronism.

Conclusions: A FAldo >10 is suggestive of MinRes with a high accuracy. FAldo, indistinctly from the presence of hyperkalemia, seems to be more accurate than aldosterone values measured during hyperkalemia, to identify hypoaldosteronism induced by MinRes as defined by the presence of ResF. Clinicians could use this FAldo to identify etiopathogenic mechanisms in hypoaldosteronism patients.

Reference: 1. Adam WR. Hypothesis: A simple algorithm to distinguish between hypoaldosteronism and renal aldosterone resistance in patients with persistent hyperkalemia. Nephrology. 2008;13:459-64.