CITRATE, MAGNESIUM AND OXALATE URINARY-EX CRETION IN NORMAL-CHILDREN

We measured 24 hour urinary excretion oi citrate (Cit), magnesium (Mg) and oxalate (Ox) in 228 normal children, 87 boys and 141 girls, aged 4-16. Urinary citrate levels varied widely and were affected by age an d sex from age 10 onwards, being significantly higher in girls. Howeve r when they were expressed as mg/kg body weight per day they were not longer affected by age but the difference between the sexes persisted: boys 9.76 +/- 5.88 mg/kg/24 hr, girls 11.26 +/- 6.10 mg/kg/24 hr (p < 0.01). The citrate/calcium index (I Cit/Ca) was 5.8 +/- 10.0 mg/mg fo r boys and 8.2 +/- 10.1 mg/mg for girls (P < 0.05). The urinary excret ion of Mg decreased with age,in both sexes and tile two sexes did not differ significantly When Mg excretion was expressed per 1.73 sq m of body surface area it no longer varied with age, the mean for the whole sample being 118 +/- 39 mg/1.73 sq m/24 hr. The Mg/Ca index (I Mg/Ca) varied widely from a 3rd centile of 0.35 mg/mg to a 97 th centile of 6 mg/mg. Oxaluria did not differ between tile sexes, it decreased sign ificantly with age but when expressed per 1.73 sq m the relationship t o age was lost. The mean result was 36.92 +/- 13.72 mg/1.73 sq m/24 hr . The Cit/cr, Mg/cr and Ox/cr ratios measured on a spot urine sample d id not correlate well enough with 24 hour urinary excretion to make th em useful substitutes for 24 hour collection.