PLE-4771

Which diagnostic procedure should be performed to investigate the possible cause of the repeated infections in a 6-year-old male patient who was admitted due to flank pain, persistently high fever, and vomiting? The urinalysis revealed WBC 15-20, RBC 3-5, WBC casts, (-) crystals, and (+) leukocyte esterase. Additionally, the patient had experienced 2 previous episodes of UTI over the past month.