Evidence for the suitability of Spot urines for selective screening in children was obtained by comparing the 24-hour urinary oxalate excretion with the ratio of urinary oxalate to creatinine [mmol/mol] in spontaneously voided urine samples. Spot urines of 169 healthy children aged l day to 13 years were analysed in order to establish reference values for the urinary oxalate/creatinine ratio in relation to age and body surface area. Oxalate was measured by automated ion chroraatography. Results showed an inverse relationship between the oxalate/creatinine ratio and age. The highest ratios, 131 ± 57 mmol/mol (mean ± 2 SD), were found in infants. At age two years, the ratio was 84 ± 55, at age five years 56 ± 35, and for children older than ten years 42 ± 31. This finding can be explained by the gain of muscle mass and hence increased creatinine productiori with increasing age. Data for the urinary oxalate/creatinine ratio are presented according to body surface area for the assessment of children with abnormal growth. In 19 urine samples from nine patients with primary hyperoxaluria, the oxalate/creatinine ratio greatly exceeded (286-2022 mmol/mol) the above reference ranges. We therefore propose the determination of the oxalate/creatinine ratio in spot urines for the selective screening for hyperoxaluria in children with nephrocalcinosis or urolithiasis.

Summary:Evidence for the suitability of Spot urines for selective screening in children was obtained by comparing the 24-hour urinary oxalate excretion with the ratio of urinary oxalate to creatinine [mmol/mol] in spontaneously voided urine samples. Spot urines of 169 healthy children aged l day to 13 years were analysed in order to establish reference values for the urinary oxalate/creatinine ratio in relation to age and body surface area. Oxalate was measured by automated ion chroraatography. Results showed an inverse relationship between the oxalate/creatinine ratio and age. The highest ratios, 131 ± 57 mmol/mol (mean ± 2 SD), were found in infants. At age two years, the ratio was 84 ± 55, at age five years 56 ± 35, and for children older than ten years 42 ± 31. This finding can be explained by the gain of muscle mass and hence increased creatinine productiori with increasing age. Data for the urinary oxalate/creatinine ratio are presented according to body surface area for the assessment of children with abnormal growth. In 19 urine samples from nine patients with primary hyperoxaluria, the oxalate/creatinine ratio greatly exceeded (286-2022 mmol/mol) the above reference ranges. We therefore propose the determination of the oxalate/creatinine ratio in spot urines for the selective screening for hyperoxaluria in children with nephrocalcinosis or urolithiasis.

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