Question

Struvite stones are formed in kidneys as a result of which of the following?

• A. \( \text{Urinary tract infection} \)
• B. \( \text{Gout} \)
• C. \( \text{Hereditary xanthinuria} \)
• D. \( \text{Hypercalcaemia} \)

Hint:

\textbf{Nephrology: Kidney Stones.} Remember the different types of kidney stones and their associated risk factors. Struvite stones are unique in that their formation is strongly linked to UTIs with urease-producing bacteria and alkaline urine.

Answer 1

The Correct Option is A

Struvite stones, also known as infection stones or triple phosphate stones, are a type of kidney stone composed of magnesium ammonium phosphate (\(MgNH_4PO_4 \cdot 6H_2O\)). Their formation is strongly associated with urinary tract infections (UTIs) caused by urea-splitting bacteria, such as *Proteus*, *Klebsiella*, *Pseudomonas*, and *Staphylococcus*. These bacteria produce the enzyme urease, which hydrolyzes urea in the urine into ammonia (\(NH_3\)) and carbon dioxide (\(CO_2\)). The increase in ammonia leads to an elevation of the urinary pH, making it more alkaline. In this alkaline environment, the solubility of magnesium ammonium phosphate decreases, leading to its precipitation and the formation of struvite stones. These stones can grow rapidly and often form large, staghorn calculi that fill the renal pelvis and calyces. Let's briefly look at why the other options are incorrect: Gout: Gout is a metabolic disorder characterized by hyperuricemia (elevated uric acid levels) and the deposition of monosodium urate crystals in joints and other tissues, including the kidneys (uric acid stones). It is not directly involved in the formation of struvite stones. Hereditary xanthinuria: This is a rare genetic disorder characterized by a deficiency in xanthine oxidase, leading to the accumulation of xanthine in the urine and the formation of xanthine stones. It is not related to struvite stone formation. Hypercalcaemia: Elevated levels of calcium in the blood can increase the risk of calcium-based kidney stones (e.g., calcium oxalate, calcium phosphate). While UTIs can sometimes occur in individuals with hypercalcaemia, hypercalcaemia itself is not the primary cause of struvite stones. Therefore, struvite stones are formed in the kidneys as a direct consequence of urinary tract infections with urea-splitting bacteria.