Kidney Stones

Enteric Hyperoxaluria is Caused by Fat Malabsorption

February 2010

This slide depicts the pathways that mediate enteric hyperoxaluria. One reason oxalate is not usually readily absorbed from the gut is that it is complexed with calcium, to a large degree. Ordinarily, little fat reaches the colon. However, in fat malabasorptive states fatty acids reach the colon and bind calcium, thus freeing up oxalate for absorption. Bile acid malabsorption might also contribute by injuring intestinal cells and increasing colonic permeability. Common causes of enteric hyperoxaluria include the now historical jejunoileal bypass, as well as the modern bariatric procedure Roux en Y bypass. Patients with inflammatory bowel disease, pancreatic insufficiency, and intestinal resection for any cause can also develop enteric hyperoxaluria, if the colon is intact. Even the lipid lowering drug Zetia, which blocks intestinal cholesterol absorption, has been associated with increased urinary oxalate levels.

Treatment for enteric hyperoxaluria includes adequate hydration, since these patients often have some degree of diarrhea and gastrointestinal losses; a low fat, low oxalate diet; and calcium dosed with meals to bind up oxalate. Cholestryamine or other bile acid sequestrants might be helpful in some patients. Urinary citrate is also often low due to gastrointestinal alkali losses, and should also be repleted.

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Jump to section:

• Introduction
• Kidney Stones
• Why do Kidney Stones Form?
• Genetics and Environment
• Not All Stones are Created Equal: Stone Analysis is Very Helpful
• Laboratory Evaluation
• Supersaturation Index
• Components of the Urinary Supersaturation Profile
• Uses of Urinary Supersaturation
• Common Features Increase Urinary Supersaturation in Patients with Idiopathic Calcium Oxalate Nephrolithiasis
• "Conservative" Dietary Recommendations for Calcium Oxalate Stone Formers
• Causes of Hypercalciuria
• Genetic Hypercalciuria
• Genetic Hypercalciuria: Treatment
• What is Oxalate?
• Hyperoxaluria: What is the Relevant Concentration?
• Oxalate Balance on a Typical Western Diet
• Enteric Hyperoxaluria is Caused by Fat Malabsorption
• Control of Urinary Citrate: Largely Due to Systemic Acid Base Balance
• Treatments for Enteric Hyperoxaluria
• Low Urinary Citrate
• Hyperuricosuria is a Risk Factor for Calcium Oxalate Stones
• Uric Acid is Very Insoluble at Low pH
• Calcium Phosphate is Very Insoluble at High pH!
• Cystine Stones
• Struvite stones
• Questions?