Pediatric reference intervals for random urine calcium, phosphorus and total protein

The aim of this study was to establish age appropriate reference intervals for calcium (Ca), phosphorus (P) and total protein (UTP) in random urine samples. All analytes were measured using the Roche MODULAR P analyzer and normalized to creatinine (Cr). Our study cohort consisted of 674 boys and 728 girls between 7 and 17 years old (y.o.), which allowed us to determine the central 95% reference intervals with 90% confidence intervals by non-parametric analysis partitioned by both gender and 2-year age intervals for each analyte [i.e. boys in age group 7–9 years (7–9 boys); girls in age group 7–9 years (7–9 girls), etc.]. Results for the upper limits of the central 95% reference interval were: for Ca/Cr, 0.27 (16,17 y.o.) to 0.46 mg/mg (7–9 y.o.) for the girls and 0.26 (16,17 y.o.) to 0.43 mg/mg (7–9 y.o.) for the boys; for P/Cr, 0.85 (16,17 y.o.) to 1.44 mg/mg (7–9 y.o.) for the girls and 0.87 (16,17 y.o.) to 1.68 mg/mg (7–9 y.o.) for the boys; for UTP/Cr, 0.30 (7–9 y.o.) to 0.34 mg/mg (10–12 y.o.) for the girls and 0.19 (16,17, y.o.) to 0.26 mg/mg (13–15 y.o.) for the boys. Upper reference limits decreased with increasing age, and age was a statistically significant variable for all analytes. Eight separate age- and gender-specific reference intervals are proposed per analyte.