Moderate renal impairment does not preclude the accuracy of 24 hour urine normetanephrine measurements for suspected pheochromoctyoma.

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24 hour urine nor/metanephrine(urine NM-MN) measurements are a recommended first step in pheochromocytoma diagnosis. We hypothesized the presence of renal impairment(CKD) significantly confounds the results obtained in a UNM-UMN collection, giving artificially lower measurements.Retrospective review of a comprehensive laboratory database with all urine NM-MN results from Southern Alberta from 2010-2018 (n=15,505). After excluding high probability pheochromocytoma cases, results from patients with three levels of CKD (n=796) were compared to those without CKD to determine the potential CKD effect.All patients having urine NM-MN collection during the time period, irrespective of ordering physician or test indication.Urine NM-MN was measured by liquid chromatography-tandem mass spectrometry and glomerular filtration rate determined within a median of 1.9 days, as estimated by CKD-EPI equation.In subjects with mild-to-moderate renal impairment, there was no continuous gradient between subnormal renal function and urine NM-MN measures. When the estimated GFR was < 15 ml/min/m2, the hypothesized effect on lowered urine NM-MN became apparent.A 24 hour urine NM-MN measurement is unlikely to be affected by mild-to-moderate renal impairment and may be used as a reliable diagnostic test. With more advanced renal impairment, CKD-specific reference ranges or an alternative test may be needed.

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