SUN-LB96 Basal Contralateral Aldosterone Suppression Is Rare in Lateralized Primary Aldosteronism and Can Be Useful in Predicting Surgical Outcome

Background: Adrenal venous sampling (AVS) is performed to distinguish between unilateral or bilateral source of aldosterone in primary aldosteronism (PA). Unilateral aldosteronomas should lead to suppression of renin and contralateral (CL) aldosterone secretion, assessed by the CL suppression ratio. We recently found that CL aldosterone suppression was relatively rare using the ratio of basal aldosterone concentration of the opposite adrenal vein/periphery (A(OPP)/A(P)) in contrast to the traditional cortisol-corrected aldosterone ratio ((A/C)(OPP)(A/C)(P)). Pathology studies showed frequent zona glomerulosa (ZG) hyperplasia adjacent to a dominant aldosteronoma, which could also indicate probable ZG hyperplasia in the CL adrenal. The ratio of basal CL suppression could be a usefull parameter to predict cure following unilateral adrenalectomy (UA), but controversy remains in the literature. Objectives: 1. To evaluate the prevalence of basal CL suppression using the A(OPP)/A(P) ratio as compared to the (A/C)(OPP)/(A/C)(P) ratio at previously established cut-offs. 2. To determine the best cut-off to predict clinical and biochemical surgical cure in two Canadian referral centers. 3. To compare the accuracy of the A(OPP)/A(P) ratio to the basal lateralization ratio (LR) and the post-ACTH LR in predicting the surgical outcome. Methods: 330 patients with PA and successful bilateral simultaneous basal and post-ACTH stimulated AVS (selectivity index >2 basally and >5 post-ACTH) were included; 124 patients found to be lateralized underwent UA. The follow-up data were evaluated for clinical and biochemical cure at 3 and 12 months using the PASO criteria. Results: Using A(OPP)/A(P) and (A/C)(OPP)/(A/C)(P) at the cut-off of 1, the prevalence of CL suppression is 6% and 45%, respectively. The median CL suppression ratio is 2.3 (1.3-5.1) in lateralized cases of PA using A(OPP)/A(P). Using ROC curves, the A(OPP)/A(P) ratio is associated with clinical cure at 3 and 12 months and biochemical cure at 12 months. (A/C)(OPP)/(A/C)(P) is associated with biochemical cure only. The cut-offs for A(OPP)/A(P) offering the best sensitivity and specificity for clinical and biochemical cures at 12 months are 2.15 (Se 63% and Sp 71%) and 6.15 (Se 84% and Sp 77%), respectively. Basal LR and post-ACTH LR are associated with clinical cure but only the post-ACTH LR is associated with biochemical cure. Conclusions: Basal CL suppression defined by the A(OPP)/A(P) ratio is rare and incomplete compared to the traditional (A/C)(OPP)/(A/C)(P) ratio in lateralized cases of PA. This may reflect the frequent micronodular hyperplasia adjacent to dominant aldosteronomas and possibly in the CL adrenal. Basal CL aldosterone suppression may predict clinical postoperative outcome, but with modest accuracy.