Bladder contractility index in posterior urethral valve: A new marker for early prediction of progression to renal failure.

INTRODUCTION: Posterior urethral valve (PUV) is the most common cause of pediatric end stage renal disease (ESRD), imposing a major health burden on medical community caregivers and adversely affecting the quality of life of patients. Chronic kidney disease (CKD) stage III or estimated GFR of <60 mL/min/1.73 m2 is known to be associated with more adverse renal, cardiovascular, and clinical outcomes. Thus, it is desirable to identify factors predicting the rapid and early progression of disease. In the present study, baseline characteristics and urodynamic study (UDS) parameters of boys with PUV are correlated with CKD progression to IIIB or more.

AIMS AND OBJECTIVES: To study the correlation of bladder contractility index (BCI) with development of CKD stage IIIB (eGFR of <45 mL/min/1.73 m2 ) or more in boys with PUV.

METHODOLOGY: Baseline characteristics and demographical variables of 270 boys with PUV who underwent valve fulguration at the hospital between 2000 and 2010 were recorded and certain UDS parameters in follow-up were noted such as bladder contractility index (BCI = PdetQmax + 5 Qmax), end filling pressure (EFP), compliance (ΔC), bladder outlet obstruction index (BOOI = Pdet Qmax - 2 Qmax), and bladder volume efficiency (BVE = Voided volume/total capacity). Fate of patients in follow-up was checked in December 2015.

RESULTS: Mean follow-up period was 8.5 years (range 5-15) and median age of patients at the time of evaluation was 5.8 years. At the end of the study, 21.8% (59/270) of patients had progressed to CKD stage IIIB or more (primary end point). Cox regression analysis was applied to risk factors predicting development of CKD stage IIIB. In the multivariate model, bladder contractility index (BCI) (HR 0.8; p = 0.004), end filling pressure (EFP) (HR 2.1; p = 0.010), and compliance (ΔC) (p = 0.020) were significantly associated with the event (i.e. an eGFR of <45 mL/min/1.73 m2 ), whereas BOOI (p = 0.053) and bladder BVE (p = 0.267) were not. ROC cut-off level for BCI predicting the primary end point was 75 (AUC ± SE, 0.73 ± 0.03, sensitivity of 78.2%, and specificity of 62.5%).

CONCLUSION: In a well performed UDS, BCI may be a useful tool for early detection of boys with PUV who are likely to progress to CKD stage IIIB or more.