The Utility of Relative Aldosterone Secretion Index Combined with Saline Infusion Test Parameters: A Diagnostic Method in Subtype Prediction of Primary Aldosteronism

Background: Adrenal venous sampling (AVS) for subtyping of primary aldosteronism (PA) is a challenging procedure with an unsatisfying bilateral success rate, which leads to a nondiagnostic result. On any side where AVS is successful, the relative aldosterone secretion index (RASI) can imply the status of aldosterone production, and the postsaline infusion test (SIT) aldosterone level may further provide information in differentiating unilateral diseases from bilateral ones. Objectives: We have illustrated a validated diagnostic method that combines the interpretation of RASI with the post-SIT aldosterone level (RASI + SIT), which may help predict the subtype of PA. Materials and Methods: Data from 33 patients with suspicious PA who underwent SIT and AVS were retrospectively reviewed. AVS data were viewed as both right and left sides as each side had their own RASI independently. Diagnostic agreement between lateralization index (LI) and RASI combining SIT was examined by kappa analysis. Diagnostic performance was further validated in patients who underwent surgery by receiver operating characteristic (ROC) curve and area under the curve (AUC). Results: RASI and LI have a great diagnostic agreement (k = 0.73), and a higher diagnostic agreement (k = 0.79) was reached after the post-SIT aldosterone level was added for further differentiation. ROC curve constructed using RASI and post-SIT aldosterone level as predictors for postadrenalectomy outcome revealed an AUC = 0.99, suggesting excellent diagnostic performance. Conclusions: With proper cutoff value and assistance of post-SIT aldosterone level, RASI is a helpful diagnostic index in AVS data interpretation, even in unilaterally successful AVS, as an alternative to LI.