HOW RELIABLE IS A SINGLE MEASUREMENT OF URINARY FLOW IN THE DIAGNOSISOF OBSTRUCTION IN BENIGN PROSTATIC HYPERPLASIA

Twenty-six elderly patients with obstructive symptomatology and an ini tial low peak urinary flow rate (< 15 ml/s) were observed for 6 to 12 months. Repeated assessments were made of flow rates and residual volu mes. Within patient variation of the maximal urinary flow was signific ant; the standard deviation (SD) varied from 0.8 to 5.5 ml/s. The SD v aried with the mean peak flow rates and this suggests that the precisi on of a single determination of a patient's peak flow is inversely rel ated to the peak flow itself. In all, 333 determinations of peak flow were obtained. Only 80% were below 2 SD of the mean Siroky nomogram. M ultiple determinations were used to estimate the sensitivity rate for each patient, i.e. the proportion of peak flows that were less than 2 SD below the mean of Siroky's nomogram. The average sensitivity for al l of the flow values was 0.813 when applied to voided volumes and incr eased only slightly to 0.838 when applied to total bladder volume. Giv en a prevalence of 0.70 of obstruction ascribed to benign prostatic hy perplasia (BPH) among elderly men, the positive predictive value of an abnormally low peak flow was 0.97. A single low peak flow based on as sessment of voided volume may serve as an almost sure indication of ob struction. If a patient has a single normal peak flow rate, he still h as a 0.31 probability of having evidence of obstruction in his followi ng uroflow determinations. Using total bladder volume does not make a difference in most patients and is not worth the effort and discomfort . The only patients who require accurate residual measurements are tho se with a normal uroflow but clear-cut obstructive symptomatology or w ith borderline peak flow. The results of this study are relevant to ev eryday clinical practice and to the evaluation of studies on alternati ves to surgery in BPH.