Bladder contractility Index (BCI) is an effective Urodynamic tool in the management of patients with complex lower urinary tract symptoms. Previous studies have suggested that a BCI value above 150 denoted a good contractile power of the Detrusor and less than the above value denoted a Detrusor underactivity.
My observation suggested that this contractile index varied in women and seems lower than the current index.The Aim of this study is to derive a Bladder contractility index value for women that it would help in diagnosing detrusor underactivity.

A Retrospective study of Urodynamics traces was done in 167 women.  Patients with bothersome lower urinay tract symotoms and mixed urinary incontinence, with normal Urodynamics study was used as Control.Abnormal Urodynamics included Bladder outflow obstruction, Derusor overactivity and Detrusor underactivity or a combination ,were included. Urodynamic values of  Detrusor pressure at maximum flow pDet@Qmax and max flow ml/ sec (Qmax) were used to derive the Bladder contractility Index BCI, with the formula, pDet@Qmax+5(Qmax).

Receiver Operating Characteristic (ROC) was drawn and obtained to decide the cut off value of Bladder contractility Index BCI, which differentates good bladder contractility from Detrusor Underactivity group. Cut off value of 113.4, which gives sensitivity of 73% and specificity of 57% seems optimal. AUROC was 0.677(67%) with p value 0.001.

Bladder contractility Index in normal control group was 143.5+/- 55.8. The other  group had contractility index of  116.+/-64. p value 0.017, which is statistically significant. AUROC 67%, p=0.0001. Cut off value of  BCI was derived at 113.4, based on Youden Index, with a sensitivity of  73% and specificity of  57% . 
 Another observation made was a statistically significant p value of p=0.0001 between the normal group BCI= 143.5+/- 55 and Bladder outflow obstruction with hypocontractile bladder (or detrusor underactivity) with Impaired contractility BCI= 87+/- 37.AUROC 80% with a cut off value of BCI at 114.5, with a sensitivity of 70% and specificity of 83%.

In this cohort of women patients, Bladder contractility Index cut off value of 113.4 with a statistical significance AUROC 67%, p=0.001 with sensitivity 73% and specificity 57% seems optimal. This index value can be used to make a Urodynamic diagnosis of Detrusor Under-activity.

J Urol. 1998 Aug: 160(2): 482-6. Detrusor contraction duration as a urodynamic parameter of bladder outlet obstruction for evaluating men with lower urinarytract symptoms. Ameda K1, Steele GS, Sullivan MP, Stember D, Yalla SV.
Investig Clin Urology 2017 Jul;58(4):247-254. doi: 10.4111/icu.2017.58.4.247. Epub 2017 Jun 27. How do we diagnose detrusor underactivity? Comparison of diagnostic criteria based on an urodynamic measure. Jeong SJ1,2, Lee JK1,2, Kim KM1,2, Kook H1,2, Cho SY1,3, Oh SJ1