Endocrine Abstracts

JOINT1291

Introduction: Primary aldosteronism (PA) is a common cause of hypertension, requiring accurate subtyping for optimal treatment and minimizing cardiovascular risk. The adrenal venous sampling (AVS) is the gold standard method for subtyping; however, the upright posture test (PT) could offer potential diagnostic value despite some limitations.

Aim: To identify the optimal cut-off for aldosterone-increase during PT in our population. Additionally, to perform a parallel evaluation of CT combined with PT for PA subtyping.

Methods: This nationwide study included all patients diagnosed with PA at Landspitali National University Hospital of Iceland from 2007 throughout 2016. The diagnostic protocol involved discontinuing antihypertensives affecting the renin-angiotensin-aldosterone system for 4–6 weeks before referral. Screening was performed by measuring morning serum aldosterone (s-aldosterone), direct renin concentration, and 24-h urinary aldosterone excretion. A positive PT was defined by a >50% increase in s-aldosterone after 4 hs of standing. PA was confirmed by the saline infusion test (SIT), with post-infusion s-aldosterone >140 pmol/l indicating PA. All patients underwent adrenal CT and synacthen-stimulated AVS for subtyping. Unilateral PA was treated with laparoscopic adrenalectomy, while bilateral disease was managed with mineralocorticoid antagonists. Statistical analysis was performed using STATA and JMP.

Results: Fifty patients underwent PT during the study period, 49 of whom also underwent AVS. The median age was 54 years (IQR 13), and 49% were women. The median blood pressure at case detection was 161/96 mmHg (IQR 22/17). CT scans revealed a unilateral adrenal nodule in 45% of patients, with 68% confirmed as unilateral by AVS. One patient with bilateral nodules on CT had bilateral PA confirmed by AVS and a positive PT. ROC curve analysis (AUC = 0,75, CI 0,61-0,89) indicated that a 50% increase in s-aldosterone during PT had 45% sensitivity and 81% specificity, classifying 65% of patients correctly. The optimal cut-off was a 74% increase in s-aldosterone, correctly classifying 71% of the patients, with 59% sensitivity and 81% specificity. Combining PT with CT to predict unilateral PA yielded 32% sensitivity, 96% specificity, 88% positive predictive value and 63% negative predictive value.

Conclusions: Our study highlights the importance of defining an optimal cut-off for the population being studied. Furthermore, the results suggest that PT, particularly when combined with other diagnostic tools, can be a reliable tool for differentiating PA subtypes. Thus, PT can be valuable in centers where reliable AVS is not readily available.