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Patients requiring oral and/or enteral nutrition support for nutritional needs can form calcium oxalate (CaOx) kidney stones. Dietary oxalate, if excessive, can contribute to CaOx stones when unopposed by appropriate calcium. The oxalate concentration of oral/enteral nutrition formulas is not known. We assessed various formulas for oxalate.METHODS: Adult and pediatric oral/enteral nutrition formulas commonly used in hospitals as well as in home feeding regimens were selected. Formulas designed for oral and enteral consumption (or either) were included (table ); completely elemental (hydrolyzed) or modular formula products were not. Multiple samples (N, table) of each formula were acidified, heated, and centrifuged. Supernatants were filtered and analyzed for oxalate by ion chromatography. Oxalate concentration (mg/LAESD), relative standard deviation (SD) between samples (coefficient of variation; CV), and calcium:oxalate ratios (mg:mg/L of formula) were calculated.RESULTS: Of 35 formulas analyzed, 9 were excluded due to inconsistent results and high CVs. Results for the 26 remaining formulas are shown (table ). Oxalate concentration ranged from 4-140 mg oxalate/L of formula. Due to highly variable calcium content, calcium:oxalate ratios varied widely between formulas (from 0-286) with lower ratios suggesting higher potential for oxalate absorption. There was no difference between mean oxalate concentration of enteral vs. oral formulas (45 vs. 46 mg/L; P¼0.92). Formulas designated for enteral use tended to have lower relative SDs (mean CV 16% vs. 21% for oral formulas), likely due to the generally more complex matrix of oral formulas, which contributed to more analytical variability. Depending on the formula, a patient requiring 1.5 L daily could obtain anywhere from 12-150 mg oxalate.CONCLUSIONS: Patients requiring oral and/or enteral nutrition support are at risk for a high exogenous oxalate load depending on the formula ingested and on the bioavailability of oxalate. Patients with a history of or at high risk for urolithiasis would benefit from strategies to reduce the bioavailability of oxalate and urinary oxalate excretion, which may include supplemental calcium with feedings or use of an appropriate lower oxalate formula.

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