Establishment of adult reference interval of oxalate in spot urine using real-world data.

Background: Hyperoxaluria, characterized by excessive oxalate production, can be attributed to high dietary oxalate intake, genetic disorders affecting oxalate metabolism, or certain intestinal diseases. Despite its clinical significance, there is a paucity of comprehensive discussions regarding the reference interval (RI) for oxalate levels in spot urine samples. This study aims to establish an appropriate adult RI for oxalate in spot urine to enhance the interpretation of clinical data.

Methods: Between January 2021 and July 2021, a cohort of 608 adults aged 19 to 85 years undergoing routine physical examinations was recruited to establish the RI. Additionally, 381 adults with complete datasets were analyzed to examine variables influencing the urinary oxalate/urinary creatinine (UOA/UCr) ratio. Urinary oxalate levels were quantified using a high-performance liquid chromatography assay assured by a proficiency testing from the College of American Pathologists.

Results: The study established sex- and age-specific Ris for the UOA/UCr ratio. For males, three age-specific partitions were identified: 19-29 years (8.499-54.39 mmol/mol), 30-39 years (10.25-61.29 mmol/mol), and ≥ 40 years (12.13-68.69 mmol/mol). In contrast, for females, two age-specific partitions were required: 19-39 years (11.03-64.93 mmol/mol) and ≥ 40 years (11.00-93.84 mmol/mol). UALB/UCr and UREA were recognized as key confounding factors in linear regression that could account for the differences in the UOA/UCr ratio in people.

Conclusion: Determining adult RI of oxalate in spot urine is crucial for diagnosing hyperoxaluria. Our sex and age-specific reference intervals will be beneficial for hyperoxaluria screening. The findings regarding the relationship between variables support explaining the variation of UOA/UCr ratio in individuals.