Adrenal vein sampling is used to establish the origins of excess production of adrenal
hormones in primary
aldosteronism. Correct
catheter positioning is confirmed using adrenal vein measurements of
cortisol, but this parameter is not always reliable. Plasma
metanephrine represents an alternative parameter. The objective of our study was to determine the use of plasma
metanephrine concentrations to establish correct
catheter positioning during adrenal vein sampling with and without
cosyntropin stimulation. We included 52
cosyntropin-stimulated and 34 nonstimulated sequential procedures. Plasma
cortisol and
metanephrine concentrations were measured in adrenal and peripheral venous samples. Success rates of sampling, using an adrenal to peripheral
cortisol selectivity index of 3.0, were compared with success rates of
metanephrine using a selectivity index determined by receiver operating characteristic curve analysis. Among procedures assessed as selective using
cortisol, the adrenal to peripheral vein ratio of
metanephrine was 6-fold higher than that of
cortisol (94.0 versus 15.5; P<0.0001). There were significant positive relationships between adrenal to peripheral vein ratios of
cortisol and
metanephrine for
cosyntropin-stimulated samplings but not for nonstimulated samplings. Receiver operating characteristic curve analysis indicated a plasma
metanephrine selectivity index cutoff of 12. Using this cutoff, concordance in sampling success rates determined by
cortisol and
metanephrine was substantially higher in
cosyntropin-stimulated than in nonstimulated samplings (98% versus 59%). For the latter procedures, sampling success rates determined by
metanephrine were higher (P<0.01) than those determined by
cortisol (91% versus 56%). In conclusion,
metanephrine provides a superior analyte compared with
cortisol in assessing the selectivity of adrenal vein sampling during procedures without
cosyntropin stimulation.