MON-198 Cosyntropin Stimulation on Adrenal Venous Sampling Obscure Surgically Curable Primary Aldosteronism

Context: While it has been shown that ACTH stimulation during adrenal venous sampling (AVS) for primary aldosteronism (PA) leads to correct lateralization, others showed opposite results. Whether to use ACTH stimulation during AVS for the subtype diagnosis of PA remains unsolved. Objectives: Our purpose of this study is to evaluate the clinical implications of ACTH stimulation during AVS in terms of surgical outcomes. Design and settings: Among JRAS cohort, we allocated 314 patients with both basal and ACTH-stimulated AVS data who underwent adrenalectomy to 3 groups: basal lateralization index (LI)≥2 with ACTH-stimulated LI ≥4 on the ipsilateral side (Unilateral (U) to U group, n=245); basal LI <2 with ACTH-stimulated LI ≥4 (n=15); basal LI≥2 with ACTH-stimulated LI <4 (U to Bilateral (B) group, n=54). We compared surgical outcomes among the groups. Results: Compared with the U to U group, the U to B group had poor clinical and biochemical outcomes and low rates of adrenal adenoma as a pathological finding. All patients in the U to Bgroup with clinical and biochemical benefits however had adrenal adenoma as a pathological finding and could be well differentiated from those with poor surgical outcome via basal LI, but not ACTH-stimulated LI. A receiver operating characteristic curve analysis demonstrated that the cut-off value of 8.3 showed the specificity of 84% for the prediction of good surgical outcome in U to B group.These results were similar even when we defined each group based on a cut-off value of 4 for basal LI. Although, the basal plasma aldosterone concentration (PAC) in the adrenal veins on both dominant and non-dominant sides among patients with better surgical outcome in the U to B group were not significantly different from those in the U to U group, there was a significant difference in the ACTH-stimulated PAC on the dominant side. Conclusions: We demonstrated novel findings showing that patients in the U to B group were shown to be comprised of 2 groups with good and poor surgical outcomes, and basal LI was useful in identifying PA patients with good surgical outcome in U to B group. The low expression level of MC2R receptor on aldosterone-producing adenoma (APA) might be the explanation of the weak response in aldosterone level in a proportion of surgically curable APA cases. These findings point to the important fact that ACTH stimulation on AVS obscure surgically curable cases of PA.