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Urinary NGAL Levels Correlate with Differential Renal Function In Patients with Ureteropelvic Junction Obstruction Undergoing Pyeloplasty

Sunday, October 21, 2012: 1:34 PM
Grand Ballroom B (Hilton Riverside)
Nicholas G. Cost, M.D.1, Paul H. Noh, MD1, Prasad Devarajan, MD2, Vesna Ivancic, MD1, Pramod Reddy, MD1, Eugene Minevich, MD1, Michael Bennett2 and W. Robert DeFoor Jr., MD, MPH, FAAP1, (1)Division of Pediatric Urology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, (2)Pediatric Nephrology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH

Purpose:                                                                                                                                              

Urinary obstruction from Ureteropelvic Junction Obstruction (UPJ-O) can lead to renal damage.  However, because the degree of UPJ-O detected by anatomic imaging such as ultrasound is not always related to renal injury, it can be difficult to determine which patients require prompt intervention versus those who may safely be observed.   Recent investigation has elucidated the potential benefit in patients with UPJ-O of urinary neutrophil gelatinase-associated lipocalin (NGAL), which is known to be a sensitive biomarker for acute kidney injury. The purpose of this study is to evaluate urinary NGAL levels in the affected renal pelvis and bladder of children with UPJ-O undergoing dismembered pyeloplasty.

Methods:

A prospective cohort study was performed of patients treated at a single institution with dismembered pyeloplasty from 2010-12. Urinary samples were obtained intra-operatively from the bladder and the obstructed renal pelvis. Samples were analyzed using a commercially available ELISA for NGAL.  Urinary NGAL levels were normalized to urine creatinine from the same specimen.  Normalized urinary NGAL (uNGAL) from the renal pelvis and bladder in each patient were compared using a Wilcoxon signed-rank test.  A ratio was calculated between uNGAL from the renal pelvis and bladder specimens.  This ratio was then correlated with clinical endpoints using a Pearson Correlation.

Results:

A total of 26 males and 14 females were enrolled and had both bladder and renal pelvic aspirates sent for NGAL measurement. Median age at surgery was 1.36yr (Range 0.12-18.7).  All patients had unilateral UPJ-O at the time of surgery.  Median bladder uNGAL was 15.0ng/mg (1.4-1650.8) and median renal pelvic uNGAL was 16.0ng/mg (1.31-18034.5), p=0.15.  The median ratio of renal pelvic to bladder uNGAL was 1.73 (0.16-85.3).  The median differential renal function by nucleotide renography was 47% (12-57) and the median T1/2 drainage was 29.6min (2.8-323). 

The correlation between the ratio of renal pelvic to bladder uNGAL and the following data-points were: Patient age (r=-0.031, p=0.849), T1/2 drainage (r=0.059, p=0.738), and Differential Renal Function (r=-0.489, p=0.001), Figure 1.  As a reference, the correlation between T1/2 drainage and Differential Renal Function was r=-0.415, p=0.012.

Conclusion:

We observed that a ratio of renal pelvic to bladder uNGAL correlates with the relative function of the affected kidney in the setting of unilateral UPJ-O.  In our prospective study analyzing uNGAL in patients with UPJ-O undergoing dismembered pyeloplasty we have found a significant correlation between higher renal pelvic uNGAL levels relative to bladder uNGAL and a decreased ipsilateral differential renal function.  While this initial data requires further validation, we believe it reveals potential for uNGAL as a biomarker in children with UPJ-O.

 

Figure 1: Scatter Plot of the Ratio of Renal Pelvic to Bladder uNGAL versus Ispilateral Differential Renal Function with Pearson Correlation Calculated.

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