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
Purely radilucent renal stones are 
Select and explain. 
A. Sturvite, B. Cystiene, C. Xanthine, D. Calium oxalate
C: Xanthine
Answer: C: Xanthine 
Explanation: Ans. is 'c' i.e., Xanthine Renal stone disease* Routine use of noncontast CT Scan has completely revolutionized te imaging evaluation of renal stone disease, nearly completely replacing plain radigrpahs and X urography for diagnosis of acute ureteral obstruction by renal stones.* Nephrolithiasis refers to the presence of calculi in the renal collecting system.* Nearly 10 % of the population will form a renal stone in their lifetime.* Sufficient calcium oxalate and phosphate is present in 80 % of the renal calculi for them to be radio-opaque on the plain radiographs.* Struvite (magnesium ammonium phosphate stones formed in the presence of alkaline urine and infection make up 15% of the renal calculi and also radio opaque on radiographs.* Cysteine stones make up 1 - 2% of the renal stones, and are mildly radio opaque. They are found in patients with congenital cystinuria.* The remaining 3 - 4% of the renal stones are composed of urate or xanthiene and are radiolucent on radiographs.