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
Most common predisposing factor for chronic pyelonephritis is: 
Select and explain. 
A. Diabetes mellitus, B. Renal stone, C. Posterior urethral valve, D. Vesicoureteric reflux
D: Vesicoureteric reflux
Answer: D: Vesicoureteric reflux 
Explanation: Chronic pyelonephritis is so often associated with vesicoureteric reflux that some feel that it is better named "Reflux nephropathy". It is impoant cause of renal damage and death from end - stage renal failure.