I had an ultrasound today for my left side pain. i peed before the ultrasound but was still holding 53 ml of urine. what's this mean?

Probably nothing: On an ultrasound "Normal" Adult post-void residual urine is considered <50 cc. A residual between 50-200 cc is a "gray area" of undetermined significance.Residual>200cc=abnormal. On one study, the accuracy of bladder scan ultrasounds done in a urology office showed a 9% false (+) result, i.e. the scan showed residual post-void urine but no residual on catheteriization of the bladder.