MON-294 Variability in Renin Suppression and Its Impact on Primary Aldosteronism Diagnosis

Abstract Disclosure: S. Thavaraputta: None. P. Greeviroj: None. S.J. Kerr: None. S. Sunthornyothin: None. W.W. Parksook: None. Background: Elevated or inappropriate aldosterone levels with concurrent renin suppression are the hallmarks of primary aldosteronism (PA). While intraindividual variability in aldosterone levels is well recognized in patients with overt PA, the variability of renin remains underexplored. Renin levels are influenced by multiple factors, including sodium intake, medications, and preanalytical errors, which may lead to falsely elevated renin levels, potentially excluding patients from a PA diagnosis and delaying appropriate treatment. Methods: We conducted a retrospective review of 42 patients scheduled for adrenal vein sampling (AVS) in 2023 at King Chulalongkorn Memorial Hospital, Bangkok, Thailand. Demographic and clinical data, including hypertension status, biochemical parameters, AVS results, treatment, and treatment outcomes, were collected. The primary objective was to evaluate the frequency of unsuppressed renin in clinical practice in patients with overt PA. Results: Among 42 patients, 16 (38%) were female. All patients had hypertension, with 7 (17%) classified as resistant hypertension. Hypokalemia was present in 38 (90%), while 3 (7%) presented with adrenal incidentalomas. Additionally, 5 (12%) had documented obstructive sleep apnea. On average, aldosterone levels were measured 2.2 times per patient (range: 1–5 times), while renin levels were measured 1.6 times per patient (range: 1–5 times). The median plasma aldosterone concentration (PAC) was 22.2 ng/dL (IQR: 15.8–32.7), ranging from 8.8 to 144.0 ng/dL. The median plasma renin activity (PRA) was 0.33 ng/mL/h (IQR: 0.10–0.76), with an aldosterone-to-renin ratio (ARR) of 107 (IQR: 48–165). Seventeen patients (38%) had renin measured on more than one occasion. Among them, six (35%) had at least one instance of unsuppressed renin (PRA >1 ng/mL/h). Notably, four of these six patients (67%) had lateralizing PA on AVS. None of the patients were on spironolactone at the time of screening or workup. Conclusion: In this cohort of patients with overt PA, renin variability was observed in a subset of individuals, with a significant proportion exhibiting lateralizing PA amenable to curative adrenalectomy. These findings underscore the importance of repeated biochemical evaluation in patients with a high pretest probability of PA to minimize diagnostic misclassification. Limitations of this study include the lack of preanalytical error assessment and sodium intake evaluation, both of which may contribute to renin elevation. Presentation: Monday, July 14, 2025