This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney & Ureturs, Subject name: Surgery
Composition of staghorn calculus is - 
Select and explain. 
A. Magnesium ammonium phosphate, B. Calcium oxalate, C. Uric acid, D. Cystiene
A: Magnesium ammonium phosphate
Answer: A: Magnesium ammonium phosphate 
Explanation: Ans. is 'a' i.e., Magnesium ammonium phosphate Staghorn calculi:* Staghorn calculi are composed of struvite (MAP, magnesium ammonium phosphate) and are usually seen in the setting of recurrent urinary tract infection with urease producing bacteria (e.g. Proteus, Klebsiella, Pseudomonas and Enterobacter).* Calcium phosphate combines with ammonium and magnesium to form the triple phosphate calculus* ieCalcium amnomium magnesium phosphate also k/a struvite stones.* These stones are smooth and dirty white and soltitary*, seen in alkaline urine esp with proteus infection which split urea to ammonia.* This type of calculus may enlarge to fill all or most of the renal collecting system forming a staghorn calculus.