Basal contralateral aldosterone suppression is rare in lateralized primary aldosteronism

Context: Unilateral aldosteronomas should suppress renin and contralateral aldosterone secretion. Complete aldosterone suppression in contralateral adrenal vein sample (AVS) could predict surgical outcomes. Objectives: To retrospectively evaluate the prevalence of basal contralateral suppression using Aldosterone (A)(contralateral(CL))/A(peripheral(P)) as compared to (A/Cortisol(C)(CL))/(A/C)(P) ratio in primary aldosteronism (PA) patients studied in two Canadian centers. To determine the best cut-off to predict clinical and biochemical surgical cure. To compare the accuracy of A(CL)/A(P) to the basal and post-ACTH lateralization index (LI) in predicting surgical cure. Methods: In total, 330 patients with PA and successful AVS were included; 124 lateralizing patients underwent surgery. Clinical and biochemical cure at 3 and 12 months were evaluated using the PASO criteria. Results: Using A(CL)/A(P) and (A/C)(CL)/(A/C)(P) at the cut-off of 1, the prevalence of contralateral suppression was 6 and 45%, respectively. Using ROC curves, the AcL/Ap ratio is associated with clinical cure at 3 and 12 months and biochemical cure at 12 months. (A/C)(CL)/(A/C)(P) is associated with biochemical cure only. The cut-offs for A(CL)/A(P) offering the best sensitivity (Se) and specificity (Sp) 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 LI and post-ACTH LI are associated with clinical cure but only the post-ACTH LI is associated with biochemical cure. Conclusions: In lateralized PA, basal contralateral suppression defined by Aa(CL)/A(P) is rare and incomplete compared to the (A/C)(CL)/(A/C)(P) ratio and is associated with clinical and biochemical postoperative outcome, but with modest accuracy.