The empty supine stress test as a predictor of intrinsic urethral sphincter dysfunction

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 testing. The initial evaluation involved uroflowmetry, catheterized residual urine, history, urogenital examination, and a cough stress test within 20 minutes after catheterization. Standardized multichannel urodynamic testing was performed at a follow-up appointment. Test indices were calculated 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 diagnosed in 238 subjects. A positive empty supine stress test was found to have 70% sensitivity and 90% negative predictive value for detecting very low urethral closure pressures, and 98% positive predictive value for genuine stress incontinence; in low-risk populations, the test had 95% negative predictive value for excluding urethral dysfunction. Conclusion: The empty supine stress test is easy to perform, 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 dysfunction. In low-prevalence populations, a negative test reliably excludes the presence of intrinsic urethral sphincter dysfunction. However, for high-prevalence and referral populations, the low predictive values of the test limit its usefulness.