Currently, there is no universally accepted standard nomogram for diagnosing female bladder outlet obstruction (fBOO). The Solomon-Greenwell (S-G) nomogram was introduced to diagnose fBOO based on the probability of obstruction using a pressure-flow study. The equation for the S-G nomogram in terms of the Bladder Outlet Obstruction Index in female (BOOIf) is PdetQmax – (2.2 × Qmax). This study aims to validate the clinical utility of the S-G nomogram in diagnosing fBOO among patients at Maharaj Nakorn Chiang Mai Hospital.

A retrospective review of videourodynamic study (VUDS) data was conducted at Maharaj Nakorn Chiang Mai Hospital, Chiang Mai University, between 2019 and 2025. A total of 137 female patients underwent VUDS for the evaluation of lower urinary tract dysfunction (LUTD). Female patients with neurogenic LUTD (N = 17) and those with absent detrusor contraction and/or inability to void during VUDS (N = 18) were excluded. The diagnosis of bladder outlet obstruction (BOO) was based on Nitti’s criteria, which include radiographic evidence of obstruction between the bladder neck and distal urethra along with sustained detrusor contraction. The Bladder Outlet Obstruction Index for females (BOOIf)was calculated for each included patient. The cut-off values were set at <0, >5, and >18, as referenced from the original S-G nomogram. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and the receiver operating characteristic (ROC) curve for each threshold were calculated.

A total of 104 patients were enrolled in the study, of whom 26 (25%) were diagnosed with female bladder outlet obstruction (fBOO) based on Nitti’s criteria. Primary bladder neck obstruction was the most common etiology among these patients (21/26), followed by dysfunctional voiding (4/26) and cystocele (1/26). In this population, when the cut-off value was <0 (corresponding to a <10% probability of obstruction), the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and receiver operating characteristic (ROC) area were 96.2%, 67.9%, 50.0%, 98.1%, and 82.0%, respectively. When the cut-off value was >5 (indicating a 50% probability of obstruction, with one patient not diagnosed as having fBOO), the respective values were 96.2%, 78.4%, 59.5%, 98.4%, and 87.0%. When the cut-off value was >18 (indicating a >90% probability of obstruction, with 10 patients not diagnosed as having fBOO), the values were 61.5%, 88.5%, 64.0%, 87.3%, and 75.0%, respectively.

Using a BOOIf cut-off value of <0, the probability of bladder outlet obstruction (BOO) was 1.8%, demonstrating a high diagnostic value for excluding female BOO. A BOOIf >5 exhibited good sensitivity and a high negative predictive value (NPV) for diagnosing female BOO. However, the specificity and positive predictive value (PPV) of the S-G nomogram were suboptimal. Despite these findings,Videourodynamic study (VUDS) remain the gold standard for evaluating patients with suspected BOO.