Overactive bladder index provides objective tool for diagnosing children

The OAB Index (OABI) combines three components – the uroflow index, voided volume ratio (VVR), and time to Qmax – and diagnosed OAB with an overall accuracy of 97%, report Ramesh Babu and Muthukumar Ashwin, both from Sri Ramachandra Institute of higher Education & Research in Chennai, India.

The uroflow index measured by Qaverage (average flow rate over the entire uroflow) divided by Qmax (maximum flow rate when the peak has a duration of more than 2 seconds) and time to Qmax gives a measure of urgency, while the VVR, measured by the amount of voided volume divided by the expected bladder capacity (EBC), gives an indication of voiding frequency, they explain in the Journal of Pediatric Surgery in March 2024.

The researchers compared the three uroflow parameters individually between 30 patients with OAB symptoms (median age 6.0 years; 57% boys) and 30 siblings without OAB (median age 6.5 years; 60% boys) who were matched for age and sex.

The mean uroflow index was 0.4 among children with OAB and 0.7 among those without, the mean VVR was 0.5 and 0.7, respectively, and the time to Qmax was 2.1 versus 5.2 seconds. The differences between the groups were significant in all cases.

Babu and Ashwin note that all the parameters showed a strong correlation with OAB, ranging from 0.76 for time to Qmax to 0.89 for the uroflow index. However, the strongest correlation of 0.95 was seen when all three parameters were combined. 

Based on multiple linear regressions and adjusted beta coefficients, the investigators defined a formula for the OABI of 8 (Qaverage/Qmax) + 9 (VV/EBC) + 0.5 (time to Qmax). The OABI for the participants with OAB was a mean of 8.4 points, which was significantly lower than the 16.2 points for those without OAB.

From this, they used receiver operating characteristic curves to calculate a cutoff score of 12 points, below which OAB could be diagnosed with 96% accuracy, 92% sensitivity, and 89% specificity. An OABI of 12–15 points was equivocal and above 15 points was considered normal.

When Babu and Ashwin tested the OABI in a validation set of 28 children being treated for OAB and 32 without OAB, they found that the cutoff score of 12 points detected OAB with a sensitivity of 93%, a specificity of 100%, and a positive and negative predictive value of 100% and 94%, respectively.

“We thus propose that an OABI less than 12 could be considered a marker of OAB and an indicator for starting pharmacotherapy,” say the researchers. They add: “It may also be useful to assess treatment response and assessing prognosis in children with OAB.”

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