From the Guidelines
The reference range for urine oxalate in pediatric patients is <0.46 mmol/24 h when corrected for body surface area to 1.73 m2, as stated in the expert consensus statement from Erknet and Oxaleurope 1. This value enables the interpretation of pediatric results using the adult reference range. When using a random urine sample for preliminary analysis, it is essential to normalize the results to urinary creatinine level, and acidification of the sample can be carried out in the laboratory provided the sample is kept at 4 °C after collection 1. Key considerations for urine oxalate testing in pediatric patients include:
- Proper collection technique, including acidification of the sample to prevent oxalate crystallization
- Correction of oxalate level for body surface area to 1.73 m2 for accurate interpretation
- Use of a 24-hour urine collection for optimal accuracy, although this can be challenging in younger children
- Consideration of the patient's clinical presentation, dietary factors, and other laboratory values when interpreting results 1. It is crucial to note that samples with pH >8 are unsuitable for analysis of urine oxalate, as oxalogenesis can occur in vitro under such conditions, leading to inaccurate results 1.
From the Research
Urine Oxalate Reference Range in Pediatrics
The reference range for urine oxalate in pediatrics can be determined by examining the urinary oxalate:creatinine molar ratios in normal children.
- According to 2, the mean (range) values for urinary oxalate:creatinine molar ratios are:
- Less than 1 year: 0.061 (0.015-0.26)
- 1-5 years: 0.036 (0.011-0.12)
- 5-12 years: 0.030 (0.0059-0.15)
- Greater than 12 years: 0.013 (0.0021-0.083)
- Another study 3 measured oxalate by ion chromatography and reported the following values for the oxalate:creatinine (Ox/Cr) ratio:
- The highest Ox/Cr values were measured during the 1st month of life [geometric mean 133 (range 61-280) mumol/mmol]
- The Ox/Cr ratio decreased gradually until 11 years of age [mean 24 (range 6-82) mumol/mmol]
- A study 4 determined reference percentiles for the urinary oxalate to creatinine ratios in healthy infants, children, and adolescents, and found that:
- The 95th percentile for the UOx/Cr ratio decreased with age, from 0.175 mg/mg (0.22 mol/mol) at 1 to 6 months to 0.048 mg/mg (0.06 mol/mol) from 7 years and beyond
Age-Related Changes in Urine Oxalate
The urine oxalate:creatinine ratio changes with age, with higher values observed in younger children and decreasing as age increases.
- As reported in 2 and 4, the urinary oxalate:creatinine molar ratio decreases with age, with the highest values observed in infants and the lowest values in adolescents
- The study 3 also found that the Ox/Cr ratio decreased gradually until 11 years of age
Comparison with Other Studies
Other studies have also investigated the reference range for urine oxalate in pediatrics, with similar findings.
- A study 5 established normal age and sex-related data for urinary calcium oxalate saturation in infancy and childhood, but did not report specific values for urine oxalate
- Another study 6 discussed the importance of citrate in preventing renal stone formation, but did not provide information on urine oxalate reference ranges