Reevaluating the use of metanephrine in adrenal vein sampling: a single centre retrospective study.

Optimal treatment of primary aldosteronism (PA) requires precise subtyping, usually performed by adrenal vein sampling (AVS) using cortisol to assess selectivity. Circadian and stress-induced variability or cortisol co-secretion may limit interpretability of cortisol-based assessment. It was hypothesised that metanephrine could be used as an alternative to cortisol to improve the interpretability of AVS. In this retrospective analysis of 102 consecutive patients with PA who underwent AVS, we compared cortisol- and metanephrine-based selectivity and lateralisation rates using different cut-offs. The study also included patients with repeated sampling as well as those with and without cortisol co-secretion. Using cortisol, bilaterally selective AVS was achieved in 90.2% of patients. Applying a selectivity index cut-off of ≥25 for metanephrine and ≥2 for cortisol, 83.6% of samples showed consistent selectivity classification. Non-selective samples were similarly frequent with metanephrine and cortisol (19.3 vs 18.9%). Rates of bilateral selectivity and lateralisation did not differ significantly between patients with and without cortisol co-secretion using either parameter. Lateralisation indices showed an 81% concordance between both markers. At follow-up, of six patients with discordant results operated following cortisol-based AVS (despite metanephrine indicating bilateral disease), biochemical cure was missing in one, partial in another, and complete in three patients. In conclusion, metanephrine is an alternative for AVS interpretation that might be useful in cases of limited cortisol interpretability. However, in a reference centre with optimised AVS protocols, metanephrine did not demonstrate superiority over cortisol. Given cost and availability considerations, cortisol remains the standard, with metanephrine as a supplement in selected cases.