In general the normal post-void residual urine in the bladder is less than 50 ml. But in case of old patients (of age higher than 65 years) it is acceptable upto the volume of 100 ml. But in younger people it must be less than 50 ml or else it is abnormal.
This leads to the problem of urinary retention which causes frequent urination or a feeling of incomplete emptying of bladder accompanied sometimes by the urge of overflow incontinence
Thus, if retention is upto 100 ml in old people it is normal .
