I warmly Welcome you! Thanks for consulting at my virtual clinic HCM. Post Voidal Residual Volume is the test done to see the remnant urine in the urinary bladder after voiding urine. It can be tested through bedside Ultrasonographic testing of the kidneys ureter and bladder (as did to your kid by the Radiologist). She has got significant volume of urine leftover after voiding. It is seen in cases of obstruction past-bladder (e.g. in your daughter it may be urethral stricture or in males it happens due to enlarged prostate) or some disease of the kidneys as in Chronic Kidney Disease. Next step in such a case is please make an appointment with a Urologist for proper evaluation and treatment accordingly. Hope it helps. Feel free to contact me anytime directly from my profile if needed further assistance. Regards! DR.HANIF USA