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Oxalate excretion during the first 7 weeks in very-low-birth-weight infants
Insights
Urinary oxalate excretion in very-low-birth-weight infants peaks in early weeks, nearing urolithiasis levels. This suggests an elevated risk for nephrocalcinosis in these vulnerable infants.
Area of Science:
- Neonatal Medicine
- Pediatric Nephrology
- Clinical Chemistry
Background:
- Urinary oxalate excretion reference values are not well-established for very-low-birth-weight (VLBW) infants.
- Elevated urinary oxalate may increase the risk of nephrocalcinosis in VLBW infants.
Purpose of the Study:
- To establish reference values for urinary oxalate excretion in VLBW infants.
- To investigate the relationship between urinary oxalate levels and infant age, nutrition, and gestational age.
Main Methods:
- Prospective, longitudinal study of 23 VLBW infants.
- 24-hour urine samples collected at 1, 2-3, 4-5, and 6-7 weeks of age.
- Urinary oxalate concentration measured by the oxalate oxidase method; oxalate-creatinine ratio also analyzed.
Main Results:
- Urinary oxalate excretion was highest in infants aged 2-3 weeks (median 35 mumol/kg/day).
- Oxalate levels and oxalate-creatinine ratios increased in the first 3 weeks and decreased thereafter.
- No significant effect of nutrition or gestational age on urinary oxalate parameters was observed.
Conclusions:
- Urinary oxalate excretion in VLBW infants is age-dependent, peaking in early infancy.
- Excretion levels approach those seen in urolithiasis patients, indicating a potential increased risk of nephrocalcinosis.
- Established reference ranges are crucial for monitoring VLBW infants.
Abstract:
To determine reference values, we studied urinary excretion of oxalate prospectively and longitudinally in a cohort of 23 very-low-birth-weight (VLBW) infants. The urinary oxalate concentrations were evaluated in 24-hour urine samples by the oxalate oxidase method. Urine samples were obtained at 1, 2-3, 4-5 and 6-7 weeks of age. The median oxalate amount was 24 mumol/kg body weight/day with a 10th-90th percentile range of 16-45 in the 1st week. Oxalate excretion was highest in 2- to 3-week-old infants (median: 35; percentile range: 26-56 mumol/kg body weight/day). In the 4th-5th week, the median was 24 (percentile range: 15-47) mumol/kg body weight/day and in weeks 6-7 also 24 (percentile range: 10-36) mumol/ kg body weight/day. Also, the urinary oxalate concentration as well as the oxalate-creatinine ratio showed increased values in the first 3 weeks of life and decreased values afterwards. In a multivariate analysis, nutrition or gestational age did not affect the urinary oxalate concentration, the daily amount excreted or the oxalate-creatinine ratio. The investigated parameters (oxalate amount and oxalate-creatinine ratio in urine) were significantly age dependent). The data show that urinary oxalate excretion in VLBW infants approaches levels that are in the same range as those of patients with urolithiasis. Thus the risk of nephrocalcinosis in VLBW infants may be increased.