Journal
PEDIATRIC NEPHROLOGY
Volume -, Issue -, Pages -Publisher
SPRINGER
DOI: 10.1007/s00467-023-06145-z
Keywords
Urine calcium-to-creatinine ratio; Urine phosphate-to-creatinine ratio; Urine magnesium-to-creatinine ratio; Urine uric acid-to-creatinine ratio; Hypercalciuria; Breastfeeding
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This study updated the reference values for solute/creatinine ratios of calcium, phosphate, magnesium, and uric acid in the urine of infants and young children. It found that breastfed infants had higher calcium/creatinine ratios and lower phosphate/creatinine ratios. New cutoff values for diagnosing hypercalciuria in infants based on the type of lactation were proposed.
Background Reference values for urinary calcium (Ca) and other solutes/creatinine (Cr) ratios in infants and young children are scarce. Its variation with type of lactation administered, breastfed (BF) or formula (F), is incompletely known.Methods A total of 511 spot urine samples from 136 children, aged 6 days to < 5 years, was collected. Urine was collected no fasting in infants < 18 months and first morning fasting in children aged 2.5-4 years. Urinary osmolality, Cr, urea, Ca, phosphate (P), magnesium (Mg), and uric acid (UA) were determined. Values are expressed as solute-to-Cr ratio.Results Urinary values were grouped according to the child's age: 6-17 days (G1), 1-5 months (G2), 6-12 months (G3), 13-18 months (G4), and 2.5-4 years (G5). G1 was excluded; Ca/Cr and UA/Cr (95th percentile) decreased with age (G2 vs. G5) from 1.64 to 0.39 and 2.33 to 0.83 mg/mg, respectively. The P/Cr median rises significantly with age from 0.31 (G2) to 1.66 mg/mg (G5). Mg/Cr was similar in all groups (median 0.20, 95th percentile 0.37 mg/mg). Ca/Cr (95th percentile) of BF infants was 1.80 mg/mg (< 3 months) and 1.63 mg/mg (3-5 months), much higher than F infants (0.93 and 0.90 mg/mg, respectively). P/Cr and P/Ca were lower in BF infants.Conclusions Values for urinary Ca/Cr, P/Cr, Mg/Cr, and UA/Cr in infants and children < 5 years were updated. BF infants < 6 months showed higher Ca/Cr and lower P/Cr than F infants. New cutoff values to diagnose hypercalciuria in infants < 6 months, according to the type of lactation, are proposed.Graphical abstractA higher resolution version of the Graphical abstract is available as Supplementary information
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