Urine pH is related to stone formation: which statement is true?

• A. Highly alkaline urine favors uric acid stones
• B. Acidic urine favors uric acid stones
• C. Neutral pH favors uric acid stones
• D. pH has no effect on stone formation

Answer: (B)

The key idea is how urine acidity controls uric acid solubility and stone formation. Uric acid is relatively insoluble in acidic urine, so when the urine pH is low, uric acid tends to precipitate and form crystals that can grow into stones. If urine becomes alkaline, uric acid is converted to urate, which is much more soluble, so uric acid stones are less likely to form and any existing stones may even dissolve with sufficient alkalinization. That’s why the statement that acidic urine favors uric acid stones is the correct one. In contrast, highly alkaline urine more often promotes other stone types, and pH does influence stone formation rather than being neutral or irrelevant.