Determination of reference interval (RI) of spot urinary oxalate to creatinine ratio in children of pakistani origin under six years of age: A cross-sectional study.

Background: The gold standard screening method of hyperoxaluria in children is using 24-hour urine collection. Urine collection may be cumbersome and challenging for children. Reference intervals (RI) of oxalate for the Pakistani population are not readily available. Therefore we aimed to determine the oxalate to creatinine ratio (Ox: Cr) for Pakistani children <6 years of age.

Materials And Methods: A cross-sectional study was conducted at Aga Khan University from June 2018 to October 2019. Random urine samples from apparently healthy children < 6 years were collected and stored at -30°C until analysis after adding 6M HCl. Oxalate was measured on Micro lab 300 using a kit based on oxalate oxidase principle, while creatinine was measured by kinetic Jaffe reaction. Data was analyzed by EP evaluator and SPSS 23. Ox: Cr ratio was calculated and reported with 90% confidence interval (CI) and interquartile range (IQR).

Results: The mean age of study subjects (n=120) was 29 ±22.3 months with an M: F ratio of 1:1. Children of various ethnicities were included from all over Karachi. The majority of the subjects were Urdu speaking (37.5%). Median Ox: Cr was 0.13(0.10). No significant difference was noted in the median Ox: Cr ratio between various ethnicities (p>0.05). It was significantly different in group I to V which was 0.25 (IQR: 0.06), 0.19 (IQR: 0.11), 0.15 (IQR: 0.04), 0.11 (IQR: 0.06) and 0.08 (IQR: 0.04) respectively (pvalue <0.001).

Conclusion: The established RIs of Ox: Cr ratio was 0.05-0.34 (90% CI). Ox: Cr ratio showed a declining trend with age. Large scale reference interval studies are encouraged, taking diet and age into consideration.