A total of 50 consecutive male patients underwent simultaneous Snap-Gauge, and full nocturnal penile tumescence evaluation with objective rigidity measurements to determine the correlation between the 2 studies. Subsequent clinical evaluation was conducted in patients in whom the 2 tests differed regarding diagnoses to determine which test more accurately predicted the clinical outcome. One patient was excluded from the study for technical reasons. Of 14 patients who had a normal Snap-Gauge evaluation, defined by breakage of all 3 bands, 12 (86%) had a normal and 2 (14%) had an abnormal nocturnal penile tumescence evaluation. A total of 28 patients failed to break any of the Snap-Gauge bands and 7 broke only 1 or 2 bands. Of these 35 patients with an abnormal Snap-Gauge study 14 (40%) had a normal and 21 (60%) had an abnormal nocturnal penile tumescence evaluation. In a subsequent clinical evaluation 1 of the 2 patients with a normal Snap-Gauge study and an abnormal nocturnal penile tumescence test reported continued inadequate sexual function and, subsequently, he received a penile prosthesis. Of the 14 patients with an abnormal Snap-Gauge study and a normal nocturnal penile tumescence test 11 were located and 8 were sexually active with adequate erections for intercourse without further medical treatment other than counseling. We conclude that the correlation between Snap-Gauge and nocturnal penile tumescence is not good, and that the nocturnal penile tumescence test is more accurate to determine the clinical diagnosis.
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