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The Combination of Urine NGAL and Urine Microbial Diversity are Specific for UTI in Children with Neuropathic Bladders
Catherine Forster, MD, MS1, Payal Banerjee, MS2, Karuna Panchapakesan, MS2, Crystal Stroud, MS2, Michael H. Hsieh, MD, PhD2.
1Children's National Medical Center, Bethesda, MD, USA, 2Children's National Medical Center, Washington, DC, USA.

Background: Children with neuropathic bladders frequently have bacteriuria. However, accurately diagnosing a urinary tract infection (UTI) in these children is difficult: urine cultures are frequently positive, and traditional markers of UTI (e.g. pyuria) are often present in the absence of symptoms. Given the risks of untreated UTI, including worsened infection and renal scarring, children with neuropathic bladder frequently receive unnecessary antibiotics. A marker that can help determine when it is safe to avoid antibiotics is needed. Diagnostic methods that capitalize on the interaction between the bacteria within the urine, i.e. the urinary microbiome, and the host urothelium may serve this role. Chao1, a measure of diversity of the urinary microbiome, is decreased in patients who develop UTI. Urine neutrophil gelatinase-associated lipocalin (uNGAL), a protein that is part of the innate immune system, is elevated in UTI. The objective of this study was to determine the predictive accuracy of a combination of elevated uNGAL and decreased Chao1 for the diagnosis of UTI in children with neuropathic bladders.
Methods: Cross sectional study of children with neuropathic bladders who had a urine culture sent to evaluate for UTI. UTI was defined as all 3 of the following: 1) >50,000 CFU/ml of a uropathogen in urine culture, 2) >10 urinary white blood cells/high-power field, 3) >2 or more of the following: fever >38 C, abdominal pain, back pain, worsened incontinence, pain with catheterization, or malodorous or cloudy urine. Patients with positive cultures that did not meet these criteria were grouped as asymptomatic bacteriuria (ASB). The no UTI group was a combination of patients with either negative cultures or ASB. Urine samples were collected via catheter. Microbial DNA was isolated, and the V4 region of the 16SrRNA gene sequenced using Illumina MiSeq. Chao1 was calculated for each sample and compared between groups using non-parametric tests. uNGAL was measured by ELISA. An uNGAL level of 229 ng/ml, based upon prior work, and a Chao1 level of 150, based upon data distribution, were used as cut-off for UTI.
Results: 34 children with neuropathic bladders were included in this study, (UTI=12, ASB=18, no growth=4). The cohort had a mean (standard deviation) age of 10(6) years and was 56% male. Anorectal malformation was the most common cause of neuropathic bladders. There were no differences in age, sex, or etiology of neuropathic bladders between groups. Median Chao1 was significantly higher in patients with negative cultures compared to positive cultures (140123, 351114, p=0.03), but not different between patients with no growth, ASB, and UTI (351114, 166118, 132117, p=0.54). The combination of uNGAL and Chao1 correctly identified 95% of patients without UTI, with a sensitivity of 33% and specificity of 95%. (Table 1)
Conclusion: The combination of Chao1 and uNGAL is poorly sensitive, but highly specific, for UTI. This combination may help prevent unnecessary antibiotic use in children with neuropathic bladder for treatment of suspected UTI.

Sensitivity and Specificity of Markers of UTI in Children with Neuropathic Bladders
>10 urinary white blood cellsNGAL (ng/ml)Combination of NGAL and Chao1
Sensitivity (95% confidence interval)92% (62-100%)67% (35-90%)33% (10-65%)
Specificity (95% confidence interval)37% (17-59%)76% (50-89%)95% (77-100%)


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