<prompt> The most common cause of renal scarring in a 3 year old child is:TraumaTraumaVesicoureteral reflux induced pyelonephritis.Interstitial nephritis  <response>: Answer is C Vesicouretrial reflux induced pyelonephritis: Renal scarring is most commonly a result of chronic pyogenic infection of the kidney or chronic pyelonephritis. Chronic pyelonephritis occurs only in patients with major anatomic abnormalities, such as obstructive uropathy, struvite calculi, or, most commonly, VUR in 30 to 45 of young children with symptomatic UTI. - Mercks manual In children 10 yr, about 30 to 50 of UTIs are associated with vesicoureteral reflux VUR which can lead to renal scarring and renal insufficiency if not treated - Mercks manual Remember :Renal tuberculosis is always secondary to some primary focus elsewhere in body and occurs later in life then other forms commonly around 20-40 years age group. 