American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the relationship between ammonium production and struvite stones?

1. It decreases urine pH

2. It increases urine pH

3. It has no effect on urine pH

4. It directly causes kidney stones

The correct answer is: It increases urine pH

The production of ammonium plays a significant role in the formation of struvite stones. Struvite stones, also known as magnesium ammonium phosphate stones, are formed in alkaline urine, which can be influenced by the presence of ammonium. When ammonium is produced, particularly in cases of urinary tract infections caused by urease-positive bacteria, it leads to the hydrolysis of urea to ammonia, which contributes to a more alkaline urine pH. This increase in urine pH is conducive to the precipitation of magnesium and phosphate salts, resulting in the formation of struvite stones. Understanding the chemical composition and the factors that lead to the formation of struvite stones is important for managing and preventing urolithiasis, particularly in patients with recurrent urinary tract infections. Recognizing the relationship between ammonium production, urine pH, and struvite stone formation can help guide appropriate treatment strategies and dietary recommendations.