Subtyping of Primary Aldosteronism in Partial Adrenal Vein Sampling: The Relative Aldosterone Secretion Index

Expanded screening with the aldosterone-renin ratio has improved detection of primary aldosteronism, the most common surgically curable cause of arterial hypertension. However, identification of surgically curable primary aldosteronism remains constrained by technical limitations of subtyping by adrenal vein sampling (AVS), as bilateral selectivity often fails. Although alternative biomarkers superior to cortisol may help reduce this rate, currently, the failure to achieve bilateral selectivity precludes calculation of the lateralization index and, thus, diverts patients toward lifelong medical therapy. Recent advances have established the relative aldosterone secretion index (RASI) as a physiologically grounded strategy to interpret partially successful AVS. By quantifying aldosterone secretion from each adrenal gland relative to peripheral values and incorporating contralateral suppression, RASI-based interpretation can rescue many AVS studies by enabling subtyping under unilateral selectivity with 80% concordance with the lateralization index, when available. Postoperative outcomes following RASI-guided adrenalectomy approximate those achieved after fully selective AVS, with biochemical cure rates of 85% to 90% and blood pressure improvement in 65% to 75%. Studies published over the past 3 years have clarified factors influencing RASI performance, including cosyntropin stimulation, variations in aldosterone secretion, and the limited utility of cross-sectional imaging alone for subtype classification. Collectively, the available data support the incorporation of RASI into contemporary AVS interpretation algorithms. As primary aldosteronism management enters a postdetection era, subtyping has emerged as the principal bottleneck to definitive cure. RASI provides a pragmatic, evidence-based means to overcome the imperative dependence on bilateral selectivity while preserving diagnostic accuracy, thereby improving access to adrenalectomy and associated cardiovascular benefits.