oxalatetocreatinine

Oxalate-to-creatinine ratio, or the oxalate-to-creatinine ratio, is a laboratory measure of the amount of oxalate excreted in urine relative to the amount of creatinine. It is typically expressed as millimoles of oxalate per millimole of creatinine or as milligrams of oxalate per gram of creatinine. The ratio helps adjust for urine concentration in spot urine samples and is used to evaluate urinary oxalate excretion without requiring a 24-hour collection.

Clinical uses include the evaluation of hyperoxaluria, a condition linked to calcium oxalate kidney stones and potential kidney damage. The ratio can help distinguish elevated urinary oxalate due to dietary intake or intestinal absorption from excess endogenous production, including inherited disorders such as primary hyperoxaluria. It may also be used to monitor therapies aimed at reducing oxalate burden or to assess risk after interventions such as bariatric surgery.

Measurement typically uses a random or first-morning urine sample analyzed for oxalate and creatinine. Oxalate is measured by enzymatic or colorimetric methods, while creatinine is measured by Jaffe or enzymatic methods. The ratio is calculated by dividing the oxalate value by the creatinine value, with unit expressions depending on the reporting method. Some laboratories report the ratio as milligrams of oxalate per gram of creatinine.

Interpretation: Higher-than-normal ratios indicate increased urinary oxalate relative to creatinine and may reflect hyperoxaluria. Reference ranges are laboratory-specific and depend on age, sex, and method. Ratios should be interpreted in the context of dietary intake and renal function, as single spot measurements can be influenced by meals, hydration, or gastrointestinal issues.

Limitations: The ratio is not diagnostic on its own and can be affected by sample timing, urine dilution, and assay variability. Dietary oxalate, vitamin C intake, and certain medications can alter excretion. Confirmatory testing with 24-hour urine collections or genetic evaluation may be necessary for suspected primary hyperoxaluria. Related topics include hyperoxaluria, calcium oxalate nephrolithiasis, and primary hyperoxaluria.