Urinary excretion of calcium, phosphate, magnesium, and uric acid in healthy infants and young children. Influence of feeding practices in early infancy.

Abstract

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. A total of 511 spot urine samples from 136 children, aged 6days to < 5years, was collected. Urine was collected no fasting in infants < 18months and first morning fasting in children aged 2.5-4years. Urinary osmolality, Cr, urea, Ca, phosphate (P), magnesium (Mg), and uric acid (UA) were determined. Values are expressed as solute-to-Cr ratio. Urinary values were grouped according to the child's age: 6-17days (G1), 1-5months (G2), 6-12months (G3), 13-18months (G4), and 2.5-4years (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 0.83mg/mg, respectively. The P/Cr median rises significantly with age from 0.31 (G2) to 1.66mg/mg (G5). Mg/Cr was similar in all groups (median 0.20, 95th percentile 0.37mg/mg). Ca/Cr (95th percentile) of BF infants was 1.80mg/mg (< 3months) and 1.63mg/mg (3-5months), much higher than F infants (0.93 and 0.90mg/mg, respectively). P/Cr and P/Ca were lower in BF infants. Values for urinary Ca/Cr, P/Cr, Mg/Cr, and UA/Cr in infants and children < 5years were updated. BF infants < 6months showed higher Ca/Cr and lower P/Cr than F infants. New cutoff values to diagnose hypercalciuria in infants < 6months, according to the type of lactation, are proposed.