SAT-279 - Diagnostic Performance of Baseline 24-Hour Urinary Aldosterone Measurement for Primary Aldosteronism

Background: Primary aldosteronism (PA) is the most common cause of secondary hypertension and is associated with increased cardiovascular morbidity. Measurement of 24-hour urinary aldosterone (24UAldo) without salt loading may be a useful, noninvasive alternative to assess aldosterone production, overcoming the high plasma aldosterone variability encountered during the diagnostic workup.

Methods: We conducted a retrospective study of patients with hypertension evaluated for PA in a tertiary referral center’s endocrinology adrenal clinic 2021-2025. After diagnostic testing was completed, patients were divided into “PA” and “non-PA” groups. PA was diagnosed based on plasma aldosterone and renin activity, confirmatory testing when available, postoperative aldosterone levels, and CYP11B2 immunostaining when applicable, and biochemical and clinical response to mineralocorticoid receptor antagonists (MRAs). The non-PA group was defined as patients with baseline aldosterone level < 5 ng/dL or a combination of aldosterone < 10 ng/dL and PRA >1 ng/mL/hr, and a lack of clinical response to MRAs when applicable. Receiver operating characteristic (ROC) analysis was performed to assess the diagnostic performance of 24UAldo, measured using commercially available LC-MS/MS assays.

Results: A total of 77 patients were included, 51 in PA and 26 in non-PA groups. The mean age (± SD) and sex distribution for the PA and non-PA groups were 55.8 ± 12.1 years, 45.1% females, and 48.4 ± 16.6 years, 69.2% females, respectively. The median 24UAldo [(interquartile range), (range)] level was significantly higher in the PA group 12.8 µg/24 h [(9.1–18.8), (2.5–124.1)] compared with the non-PA group 6.3 µg/24 h [(3.6–8.4), (1.6–13.3)]; (P < 0.001).The median (IQR) urinary sodium and potassium levels in the PA and non-PA groups were 132.5 mEq/day (121–143) and 70 mEq/day (57–81), and 165 mEq/day (143–194) and 68 mEq/day (61–81), respectively. ROC analysis demonstrated moderate diagnostic discrimination for 24UAldo, with an area under the curve (AUC) of 0.83. The optimal cut-off value to discriminate between the groups was 9.5 µg/24 h, with a sensitivity of 74.5% and a specificity of 88.5%. None of the patients in the non-PA group had a 24UAldo value >13.3 µg/24 h, corresponding to 100% specificity at this threshold. However, the PA group demonstrated a wide range of urinary aldosterone values, with some patients having values below the assay’s lower limit in the absence of hypokalemia at the time of urine collection, indicating that low baseline 24UAldo cannot reliably exclude PA.

Conclusion: Baseline 24UAldo demonstrates moderate diagnostic performance among patients being evaluated for PA. In our cohort, 24UAldo level of 9.5 µg/24 h provided the optimal cut-off for distinguishing patients with PA. Larger studies are needed to better define the role of baseline 24UAldo in evaluating patients suspected of PA.

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