Simultaneous liquid chromatography tandem mass spectrometric determination of urinary free metanephrines and catecholamines, with comparisons of free and deconjugated metabolites

ObjectiveWe introduce a novel liquid chromatographic tandem-mass spectrometric method for simultaneous measurements of urinary catecholamines and their free O-methylated metabolites, which we compare to the deconjugated metabolites.MethodsMethod performance was validated for recovery, linearity, precision and accuracy, analyte stability, ion suppression and carry over. Results from 53 patients with and 138 volunteers without pheochromocytoma were compared.ResultsAnalyte recoveries ranged from 60 to 96% and intra- and inter-assay coefficients of variation from 2.7 to 13.2%. The method showed excellent linearity over 3 orders of magnitude with analytical sensitivity sufficient to measure to 1.2 nmol/L. Free O-methylated metabolites were excreted at less than 20% the rates of the deconjugated metabolites, but were easily measureable. Increases in urinary normetanephrine in pheochromocytoma patients relative to volunteers were higher for free than deconjugated metabolites and higher for both than for norepinephrine (10 vs 5.5 vs 3.7 fold increases). In contrast, relative increases in urinary free versus deconjugated metanephrine (2.7 and 3.2) and methoxytyramine (2.1 and 1.9) did not differ, but for methoxytyramine were larger than for dopamine (1.2).ConclusionMeasurements of urinary catecholamines and their free O-methylated metabolites by our method provide potential advantages over urinary deconjugated metanephrines for diagnosis of pheochromocytoma.

► LC–MS/MS measurement of urine catecholamines and their free O-methylated metabolites
► Reference intervals for urinary catecholamines and their free O-methylated metabolites
► Utility of the LC–MS/MS method for detection of pheochromocytomas and paragangliomas
► Analytical and diagnostic advantages of measuring free vs. deconjugated metabolites
► Urinary free methoxytyramine to assess tumor dopamine production