Urinary tract infection in a 3 years male child should be attended to find out a cause. First
step is a thorough physical examination, as sometimes as trivial a cause as phimosis (non-opening of foreskin) may cause urinary infections. After the examination, the next step is ultrasonography to find any anatomical defect in urinary tract, which obviously does not seem to be there from your description. Ultrasound examination on the child has not revealed any residual urine (although I must tell you that presence of significant residual urine in children could be absolutely normal). A MCU test, usually done after 3 to 4 weeks of infection episode, has already been done, and has been found to be normal. Frankly speaking, I do not find a justification to perform an invasive investigation like urodynamic evaluation in absence of a finding on MCU or ultrasonography. I would suggest that the child be followed with urine examinations and urine cultures performed on a freshly voided midstream sample. It is not easy to collect a clean mid stream sample in a child. Another mistake is to collect the sample in morning, and delivering it to the lab after couple of hours. Both these situations may result in a false positive urine culture, and unnecessary investigations. Clinicians are sometimes forced to collect urine sample by a supra pubic aspiration or catheter collection to prove or disprove the presence of urinary tract infection.