RASI FOR UNILATERALLY SUCCESSFUL AVS CANNULATIONS - TOO GOOD TO BE TRUE?

Objective: Adrenal vein sampling (AVS) is recommended for identifying candidates for surgical treatment of primary aldosteronism (PA). The failure rate of this procedure is as high as 90% in some centers, mainly due to the failure of cannulation of the one or both adrenal veins. The relative aldosterone secretion index (RASI) has been proposed as an alternative metric to interpret AVS procedures when the adrenal vein cannulation is only unilaterally successful. The proposed RASI cutoff values with the maximum sensitivity and specificity are either >2.55 (responsible gland) or =/< 0.96 (contralateral adrenal) to identify unilateral PA (uPA). The objective of this study was to look at unilaterally successful AVS procedures in our centre and determine how many of these could be ‘salvaged’ by using the RASI. Design and method: Retrospective review - all AVS results from October 2021 to January 2025 were included. We calculated the lateralisation index (LI), the selectivity index(SI), and the RASI. Results: 1. Failure rate of 43.2% was noted out of 37 included procedures. The SI indicated failed cannulation of the right adrenal vein in 12 procedures and left adrenal vein in 4 procedures. 2. Of the patients with failed unilateral cannulation, the RASI values suggested uPA in 11 patients. The other 5 patient values indicated ‘non uPA’, i.e., diagnostic uncertainty in lateralisation. 3. Interestingly, of the 17 patients with successful bilateral cannulation and lateralisation using the LI (>2), only 5 of them also had RASI values (on both sides) indicating uPA, and all these 5 patients had LI (>5.9). Conclusions: The RASI suggests a high number of false positives for uPA when applied to patients with unilaterally successful cannulation (more than the expected uPA prevalence in PA, and more in number in comparison to RASI values from bilaterally successful procedures). A calculator that determines the pre-test probability (akin to d-dimer interpretation) may rationalise the use of RASI more widely as there is significant centre specific variability in selection of patients for AVS. The data from our center will be useful in performing future metaanalyses and external validation of the RASI.