Pediatric total fractionated metanephrines: age-related reference intervals in spot urine.

Background: Sparse metanephrines reference intervals in pediatric populations are available and different study designs and technologies/ assays used in these studies lead to hardly transferable data from a laboratory to another. The aim of this study was to update pediatric reference intervals of total fractionated metanephrines in spot urine samples, using a commercial extraction kit run on a specific high-pressure liquid chromatograph coupled with an electrochemical detector.
Methods: Four hundred and fifty-two spot pediatric urinary samples previously submitted to urinalysis were consecutively included in the study with the exclusion of children's samples with diagnosis or clinical suspicion of paraganglioma/pheochromocytoma, kidney diseases and arterial hypertension. Urinary metanephrine, normetanephrine and 3-methoxytyramine were extracted with ClinRep ^® HPLC Complete kit and run on HPLC Prominence liquid chromatograph LC-20AT (Shimadzu Italia S.r.l. Milan, Italy) coupled with Decade II electrochemical detector (Antec Scientific, Zoeterwoude, the Nederlands, provided by Alfatech S.r.l., Genoa, Italy). Results were expressed as the ratio analyte-to-creatinine.
Results: Any of the three analytes required a repartition by gender (metanephrine P=0.27; normetanephrine P=0.90 and 3-methoxytyramine P=0.18). A significant statistically inversely proportional relation with age was found for metanephrine (P<0.0001; ρ=-0.72), normetanephrine (P<0.0001; ρ=-0.75) and 3-methoxytyramine (P<0.0001; ρ=-0.83). Reference intervals were calculated as function of age.
Conclusions: This study provides pediatric reference intervals for urinary fractionated total metanephrines in spot urine calibrated on a specific instrumentation and extraction commercial kit.