Unreliable residual volume measurement after increased water load diuresis

BACKGROUND: The aim of the present study was to examine whether increased water load intake prior to ultrasound examination of the lower urinary tract, affects the measurement of postvoid residual urine volume. PATIENTS AND METHODS: Ninety four male patients with postvoid residual volumes after increased water load diuresis of more than 100 mL (PVR1) were included in the present study. All patients underwent a second PVR measurement by an urologist with a portable transabdominal bladder ultrasound scan without having received an increased water load (PVR2). A comparison of the measurements was performed and the PVR values were also correlated with other parameters, such as age, International Prostate Symptom Score, prostate volume and serum prostate-specific antigen (PSA) values. RESULTS: Postvoid residual urine volume after increased water load diuresis (PVR1) differed from that recorded after normal bladder filling and voiding at first desire (PVR2), with the former being larger than the later in every patient (P < 0.001). The PVR values, PVR1 and PVR2, were independent to patient age, symptom score prostate volume and PSA value. CONCLUSIONS: Measurement of postvoid residual volume in a relaxed patient, who voids at first desire, represents everyday life and should be the correct method of testing.