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Background: Metanephrines are biochemical markers for tumors of the adrenal medulla (e.g., pheochromocytoma) and other tumors derived from neural crest cells (e.g., paragangliomas and neuroblastomas). We describe a liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the measurement of urinary conjugated metanephrines. Methods: We added 250 ng of d3-metanephrine (d3-MN) and 500 ng of d3-normetanephrine (d3-NMN) to 1 mL of urine samples as stable isotope internal standards. The samples were then acidified, hydrolyzed for 20 min in a 100 °C water bath, neutralized, and prepared by solid-phase extraction. The methanol eluates were analyzed by LC-MS/MS in the selected-reaction-monitoring mode after separation on a reversed-phase amide C16 column. Results: Multiple calibration curves for the analysis of urine MN and NMN exhibited consistent linearity and reproducibility in the range of 10–5000 μg/L. Interassay CVs were 5.7–8.6% at mean concentrations of 90–4854 μg/L for MN and NMN. The detection limit was 10 μg/L. Recovery of MN and NMN (144–2300 μg/L) added to urine was 91–114%. The regression equation for the LC-MS/MS (x) and colorimetric (y) methods was: y = 0.81x − 0.006 (r = 0.822; n = 110). The equation for the HPLC (x) and LC-MS/MS (y) methods was: y = 1.09x + 0.05 (r = 0.998; n = 40). Conclusions: The sensitivity and specificity of the MS/MS method for urinary conjugated metanephrines offer advantages over colorimetric, immunoassay, HPLC, and gas chromatography–mass spectrometry methods because of elimination of drug interferences, high throughput, and short chromatographic run time.

clinical chemistry

Validation of Liquid Chromatography–Tandem Mass Spectrometry Method for Analysis of Urinary Conjugated Metanephrine and Normetanephrine for Screening of Pheochromocytoma