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
Stag Horn Calculus is made up of: 
Select and explain. 
A. Magnesium ammonium phosphate, B. Calcium oxalate, C. Uric Acid, D. Cysteine
A: Magnesium ammonium phosphate
Answer: A: Magnesium ammonium phosphate 
Explanation: Ans. (a) Magnesium ammonium phosphateRef Bailey and Love 27th Edition, Page 1406Triple Phosphate Stone:* Usually Calcium phosphate but sometimes is combined with ammonium and magnesium to form the triple phosphate calculus ammonium magnesium phosphate* Also, k/a struvite stone* Smooth and dirty white and solitary* Seen in alkaline urine especially with proteus infection which split urea to ammonia* This type of calculus may enlarge to fill all or most of renal collecting system forming a staghorn calculus