Oxalic Acid, 24-Hour Urine
Kidney Function marker
Oxalic Acid 24 Hour Urine
Oxalic Acid, 24-Hour Urine
A 24-hour urine collection measuring total oxalate excretion over a full day. This is the preferred test for assessing kidney-stone risk from oxalate, because it captures average excretion rather than a single-moment snapshot like the serum oxalate test. Elevated 24-hour urine oxalate (hyperoxaluria) is a major driver of calcium-oxalate stones.
PED Notes
This is the more actionable of the two oxalate tests for stone-forming athletes. It relates directly to the serum oxalate marker but reflects a full day of intake and metabolism, making it far better for diagnosing dietary or enteric hyperoxaluria. Enhanced athletes accumulate multiple risk factors: high protein and purine load, chronic dehydration from diuretics or hard training, and high-dose vitamin C. A raised 24-hour oxalate points squarely at these modifiable habits.
When high
When high (>40 mg/24h, hyperoxaluria):
Dietary and lifestyle interventions (first-line):
- Hydration -- increase fluids to achieve at least 2.5L urine output/day; the most effective single measure to lower stone risk
- Stop high-dose vitamin C -- doses above ~500mg/day convert to oxalate; a common and easily reversed contributor in supplement users
- Adequate dietary calcium with meals -- 1000-1200mg/day taken with food binds oxalate in the gut and reduces its absorption; do not restrict calcium
- Moderate high-oxalate foods -- spinach, rhubarb, beetroot, nuts, and excessive tea/chocolate
Supplements / pharmacological options:
- Potassium citrate -- prescription (typically 20 mEq 2x/day); raises urinary citrate (a natural crystal inhibitor) and urine pH; physician-supervised with potassium monitoring, particularly given AAS-related renal and electrolyte effects
- Magnesium citrate -- 200-400mg/day; inhibits calcium-oxalate crystallisation
- Pyridoxine (vitamin B6) -- can lower oxalate production in certain hyperoxaluric states; use under guidance
- Persistent marked hyperoxaluria warrants nephrology evaluation to distinguish dietary, enteric (fat malabsorption), and primary (genetic) hyperoxaluria before escalating therapy
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Frequently Asked Questions
Reference Ranges
Standard Range