LAUSR

vein to peripheral vein de fi nes the selectivity index (SI). However, with no standardized cut-off levels, this limits the applicability of AVS when cortisol is being utilized (5, 6). The use of free metanephrine (FMN) has been shown to be superior to cortisol in assessing SI (7, 8). This study shows that FMN is a better analyte than cortisol in con fi rming the correct placement of the catheter ’ s tip. The main limitation, however, was that no con fi rmatory tests were performed. Other studies have also explored the use of different analytes such as aldosterone-to-renin ratio (ARR) in combination with cortisol SI (9) and plasma metanephrines in addition to cortisol (10). While the results are promising, further research is needed to establish the utility of these markers especially in those with con fi rmed PA.