FRI130 Usefulness Of The Upright Posture Test In The Diagnosis Of Primary Aldosteronism

Disclosure: N. Younes: None. M. St-Jean: None. M. Desrochers: None. I. Bourdeau: None. A. Lacroix: None. Objectives: Renin-independent aldosterone excess characterizes primary aldosteronism (PA). We have previously shown that PA is frequently regulated by aberrant stimuli, including the upright posture stimulation test (UPT), in which plasma aldosterone concentrations (PAC) increase in a renin-independent manner. In this study, we further examined the usefulness of UPT in diagnosing PA. Methods: We conducted a retrospective analysis of the medical records of 187 adult patients who underwent an UPT as part of their evaluation for possible PA and 25 control subjects, in 2 referral university centers between January 2011 and December 2021. UPT was conducted in an ambulatory setting, mostly in patients with potential false negative or borderline results of oral/IV saline confirmation tests. UPT was performed in a fasting state, early morning, 72 hours off beta-blockers, ACE, or ARBS. Patients were in a supine posture for 1 hour, followed by ambulation for 2 hours. Blood samples were collected for PAC, renin, and cortisol, at baseline and at 30 minutes intervals during ambulation. An abnormal response was defined as a ≥50% rise in PAC with a suppressed renin (≤10.1 ng/L or ≤1 ng/mL/h) and a cortisol increase ≤50%. Results: Median age of patients was 55.0 [IQR (46.0; 63.0)], 52.4% were female. 93.6% were taking at least one antihypertensive medication and 32% had hypokalemia. 43.5% did not have adrenal nodules at imaging. 76.5% (n=143) were diagnosed with PA, based on either IV/oral sodium load or UPT. When compared to controls, PA patients had higher basal PAC and lower basal renin levels (p<.0001) and achieved a higher maximal PAC and lower maximal renin (renin (max)) in response to posture [median PAC (IQR): 802.0 pmol/L (569.0, 1244.0) in PA v/s 624.0 pmol/L (500.0, 736.0) in controls, p=0.0081 and median renin 5.0 ng/L [IQR (3.0, 8.0)] in PA v/s 27.5 ng/L in controls (19.0, 46.0); p<.0001]. Renin (max) ≤10.1 had the best sensitivity and specificity for predicting PA (90% and 92%, respectively). 95.3% of PA patients increased PAC by at least 50% on UPT (median increase 363%), while renin remained suppressed. All 42 PA patients with a false negative (PAC ≤162 pmol/L) on IV saline test had a renin (max) ≤10.1 during UPT and 97.6% increased aldosterone by at least 50%. 84% of PA patients with a borderline response (162-240 pmol/L) on IV saline test, had a renin (max) ≤10.1 and all patients increased aldosterone by at least 50%. 42 patients underwent adrenal vein sampling: 50% had lateralized PA (potassium was lower than in bilateral PA, p=0.003). However, the aldosterone and renin response to UPT did not significantly differ between the two subtypes of PA. Conclusion: A renin-independent aldosterone increase during UPT can be used to confirm PA diagnosis, which was particularly useful in patients with false negative saline loading tests. Renin-independent PAC response to UPT occurred equally in lateralized and bilateral PA. Presentation: Friday, June 16, 2023