PRESSURE-FLOW STUDIES IN THE DIAGNOSIS OF BLADDER OUTLET OBSTRUCTION - A STUDY COMPARING SUPRAPUBIC AND TRANSURETHRAL TECHNIQUES

Objective To compare suprapubic and transurethral methods of measuring intravesical pressure in a group of men undergoing investigation for lower urinary tract symptoms (LUTS), to identify which urodynamic vari ables are affected by the presence of an urethral catheter during the voiding phase, and consequently whether there is any change in the gra ding of bladder outflow obstruction (BOG) using the commonly recognise d grading systems. Patients and methods Thirty-five men with LUTS unde rwent both suprapubic and transurethral pressure-flow studies during a single session. Standard pressure flow variables were measured in all patients with both methods, enabling calculation of obstruction using the commonly used grading systems, i.e. the Abrams-Griffith number, l inear passive urethral resistance ratio (LPURR) and urethral resistanc e algorithm (URA). Results There were statistically significant differ ences between the methods in the mean values of maximum flow rate and the detrusor pressure at that maximum; 60% of men were in the same LPU RR class with either method. Using the transurethral method, 26% of pa tients increased the LPURR class by one and 6% by two classes. Using t he Abrams-Griffiths nomogram, 17% moved from a classification of equiv ocal to obstructed and 3% from unobstructed to equivocal. Using the cr iterion of a value of URA > 29, 57% were obstructed using the suprapub ic and 74% using the transurethral method. Conclusion According to the method used, there were differences in the classification of obstruct ion between the suprapubic and transurethral routes; transurethral stu dies tended to indicate greater obstruction. The interpretation of uro dynamic studies should take into account the technique used and where the route is transurethral, the smallest catheter available should be used.