Reference range for gastrointestinal oxalate absorption measured with a standardized [13C2]oxalate absorption test

Area of Science:

• Nephrology
• Gastroenterology
• Metabolic Research

Background:

• Hyperoxaluria is a key risk factor for calcium oxalate (CaOx) urolithiasis.
• Urinary oxalate originates from endogenous synthesis and gastrointestinal absorption.
• CaOx stone formers exhibit variable oxalate absorption, ranging from 2% to 50% of dietary intake.

Purpose of the Study:

• To establish reference values for intestinal oxalate absorption in healthy individuals.
• To provide a basis for interpreting oxalate absorption tests in patients with recurrent urinary stones.
• To address the lack of standardized reference data for oxalate absorption.

Main Methods:

• 120 healthy volunteers (60 male, 60 female) consumed an identical standard diet over two days.
• On day 2, participants ingested a capsule containing 0.37 mmol of non-radioactive sodium [13C2]oxalate.
• Urinary oxalate was quantified using gas chromatography-mass spectrometry; absorption was calculated as a percentage of the labeled dose.

Main Results:

• The reference range for standardized [13C2]oxalate absorption in 95% of volunteers was 2.2% to 18.5% (mean ± SD: 7.9% ± 4.0%).
• Repeatability testing in 26 volunteers showed a mean intra-individual standard deviation of 3.39% ± 1.68%.
• Significant inter-individual and intra-individual variability in oxalate absorption was observed.

Conclusions:

• Reference values for intestinal oxalate absorption have been established using a standardized protocol.
• High variability underscores the complexity of oxalate absorption and its clinical interpretation.
• These findings are essential for accurate diagnosis and management of hyperoxaluric conditions and CaOx stone disease.