This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney and ureter, Subject name: Surgery
Stone formed in alkaline urine is: 
Select and explain. 
A. Calcium oxalate, B. Calcium phosphate, C. Cysteine, D. Uric acid
B: Calcium phosphate
Answer: B: Calcium phosphate 
Explanation: Struvite stones (infection stones) - Composed of calcium, ammonium, magnesium phosphate (Triple phosphate stones). Tend to grow in alkaline urine, especially with Proteus infection and fill whole of the pelvi-calyceal system, forming staghorn calculi. Formed In high urinary concentration of ammonia. More common In women (Increased susceptibility for UTI) Increased tendency to form struvite calculi Is seen In: Foreign body In the urinary tract (Foley's catheter) and neurogenic bladder / Bladder dysfunction / Bladder outlet obstruction.