The Empty Supine Stress Test as a Predictor of Intrinsic Urethral Sphincter Dysfunction ROBERT W. LOBEL, MD, AND PETER K. SAND, MD Objective: To assess the usefulness of a proposed test for intrinsic urethral sphincter dysfunction. Methods: Subjects were included in the study if they had complaints of incontinence, did not have substantial pelvic prolapse, and had undergone multichannel urodynamic test- ing. The initial evaluation involved uroflowmetry, catheter- ized residual urine, history, urogenital examination, and a cough stress test within 20 minutes after catheterization. Standardized multichannel urodynamic testing was per- formed at a follow-up appointment. Test indices were cal- culated based on the result of the empty supine stress test, the presence of genuine stress incontinence, and maximum urethral closure pressures. Results: Three hundred four women met the inclusion criteria; 124 had a positive empty supine stress test and 180 had a negative test. Genuine stress incontinence was diag- nosed in 238 subjects. A positive empty supine stress test was found to have 70% sensitivity and 90% negative predic- tive value for detecting very low urethral closure pressures, and 98% positive predictive value for genuine stress incon- tinence; in low-risk populations, the test had 95% negative predictive value for excluding urethral dysfunction. Conclusion: The empty supine stress test is easy to per- form, inexpensive, and without significant risk. By itself, a positive empty supine stress test is essentially diagnostic for genuine stress incontinence, and in combination with a fixed urethra, it is diagnostic for intrinsic urethral sphincter dys- function. In low-prevalence populations, a negative test reliably excludes the presence of intrinsic urethral sphincter dysfunction. However, for high-prevalence and referral pop- ulations, the low predictive values of the test limit its usefulness. (Obstet Gynecol 1996;88:128-32) In the evaluation of incontinent women, the clinician must consider the diagnosis of intrinsic urethral sphinc- ter dysfunction. This condition denotes a weakened intrinsic sphincter mechanism, and may or may not be associated with urethral hypermobility. Standard vagi- From the Ezunstor~ Cmtinerm Ct’uter, Diz~isim of Urogynecology and Pelzlic Rrcut~structir~r~ Surguy, Departnmt of Obstetrics and Gynecology, Euatlstm Hospital, Nortlwestem University Medical Schoul, Ezuizstm, Illimis. nal, retropubic, or needle urethropexies do not produce satisfactory results in many women with intrinsic ure- thral sphincter dysfunction, with reported failure rates o as high as 54/o. ’ Therefore, suburethral slings have become the procedure of choice in affected patients with urethral hypermobility, whereas periurethral injections, obstructive slings, and artificial sphincters are accepted therapy for those with relatively immobile urethras. The identification of women with intrinsic dysfunction is vital in providing appropriate treatment. The diagnosis of intrinsic urethral sphincter dysfunc- tion can be made only with the aid of specialized procedures, such as urodynamic studies or videocys- tourethrography. Primary care physicians might find great utility in a simple, inexpensive test that would allow them to either include or exclude intrinsic ure- thral sphincter dysfunction as a complicating factor in genuine stress incontinence. Having noted that many patients with low urethral closure pressures leaked urine with Valsalva despite having been catheterized minutes before, we hypothesized that women with intrinsic urethral sphincter dysfunction will leak urine even with a relatively empty bladder, most likely be- cause their damaged urethra provides less resistance to increases in intra-abdominal pressure. This study was designed to test this hypothesis. Materials and Methods From January 4, 1993, to August 31, 1995, 913 consecu- tive women presented to the Evanston Continence Center for initial evaluation of their lower urogenital tract complaints. Subjects were included in this study if they had complaints of incontinence and reported for subsequent multichannel urodynamic testing. Women with pelvic prolapse to or beyond the introitus were excluded, as were those with urinary tract infections. The initial evaluation included spontaneous uroflow- metry, catheterized residual urine, urine culture and sensitivity, and a directed history and physical exami- 128 0029-7844/96/$15.00 PII SOO29-7844(96)00087-7 Obstetrics & Gynecology