Are Age and Voided Volume Sufficient to Predict Detrusor Underactivity in Women? An External Validation Study

Purpose Detrusor underactivity (DU) is a significant cause of female lower urinary tract symptoms. We aimed to externally validate a non‐invasive prediction model using age and voided volume (VV) in a tertiary center cohort. Methods This retrospective study included 450 consecutive women who underwent uroflowmetry and subsequently multichannel urodynamics (UDS) between 2014 and 2025. DU was defined by pressure‐flow criteria as in the development study. Model performance was assessed via AUC‐ROC, calibration plots, Brier scores, and Decision Curve Analysis (DCA). Results The prevalence of DU in our cohort was 16.2% (73/450), compared to 10% in the original development study. The model demonstrated poor discrimination with an AUC of 0.575 (95% CI 0.50–0.65), a significant decrease from the original reported AUC of 0.82. At the suggested cut‐off, sensitivity was 78%, but specificity was only 32%. Calibration was poor (slope = 0.134; intercept = −1.397), indicating a systematic overestimation of risk. The Brier Skill Score was negative (−0.154), and DCA confirmed that the model provided negligible net clinical benefit over the default “test‐all” or “test‐none” strategies. Conclusion Validation of the proposed model failed to demonstrate statistical reliability in our cohort. These findings suggest that the model lacks the necessary transportability to serve as a clinical screening tool for female DU, underscoring the continued need for invasive testing to ensure diagnostic accuracy.