Kidney Stones

Uric Acid is Very Insoluble at Low pH

February 2010

We will now briefly discuss other types of kidney stones. Fortunately, the urinary risk factors for each of these is more straightforward. Uric acid is very insoluble in urine with a pH less that 5.3. Hence, uric acid stones are all about having an acidic urine. Causes of acidic urine include excessive gastrointestinal losses of bicarbonate from diarrhea or illeostomies or a relatively protein rich diet such as the Atkins diet. More recently, it has been demonstrated that patients with insulin resistance or diabetes tend to have very acidic urine. The mechanism here seems to involve, at least in part, decreased renal ammoniagenesis and hence increased excretion of the daily acid load in the form of titratable acid. Treatment is fairly gratifying in that urinary alkalinization to a pH> 6 to 6.5 with oral citrate will effectively prevent uric acid crystallization, and even dissolve some pre existing uric acid stones.

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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?