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

OBJECTIVE A 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 urine NM-MN collection, giving artificially lower measurements. DESIGN Retrospective review of a comprehensive laboratory database with all urine NM-MN results from Southern Alberta from 2010 to 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. PATIENTS All patients having urine NM-MN collection during the time period, irrespective of ordering physician or test indication. MEASUREMENTS 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. RESULTS 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