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Certain factors predicative of renal scarring after first UTI
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Children with a urinary tract infection who have abnormal renal ultrasonographic results or a high fever and an etiological organism other than Escherichia coli have a high risk for renal scarring.
Nader Shaikh, MD, MPH, of the University of Pittsburgh School of Medicine in Pittsburgh, and colleagues conducted a meta-analysis of patient data from cohort studies of children who underwent renal scanning with technetium Tc 99m succimer (dimercaptosuccinic acid) at least 5 months after their first urinary tract infection (UTI). Studies with positive urine culture results were included, those with neonatal cohorts were excluded. Nine studies were included in the analysis, yielding a study cohort of 1,280 children.
Most of study participants were younger than 24 months. Approximately 48% had a temperature of at least 39°C and 8.4% of infections were from an organism other than E. coli, according to the study data.
An estimated 20% of children had an abnormal renal ultrasonographic; 29.1% of children had vesicoureteral reflux (VUR); and 4.1% had VUR of grades IV to V.
Of the 199 children (15.5%) with renal scarring, 100 (50.3%) had VUR. The proportion of children with renal scarring increased as the grade of VUR increased.
Risk factors for renal scarring, listed in descending significance, includeed grade IV or V VUR; abnormal ultrasonographic finding; grade III VUR; C-reactive protein level of more than 40 mg/L; temperature of at least 39°C; organism other than E. coli; and grade I or II VUR.
To identify variables predictive of renal scarring through univariate analysis, researchers developed and compared three increasingly invasive strategies for evaluating a first-diagnosed UTI in children. Model 1 included routinely collected information, including history, exam results, and renal ultrasonographic findings. Model 2 included all information in model 1 plus serum inflammatory markers. Model 3 included everything in model 2 plus information on the presence and degree of VUR.
A model 1 score of 2 or more had a sensitivity of 44.9% and specificity of 82.4%. A model 1 score of 2 or more predicted 68.2% of patients with a grade IV or V VUR. Subanalysis of models 2 and 3 was limited due to small sample size, but in general appeared less significant than model one, according to researchers.
“Because we included studies that were conducted at a time when [voiding cystourethrogram] was routinely recommended, we were able to assess the additional predictive ability of three increasingly invasive models. We found that using a simple model with only three clinical variables provided a reasonable screening strategy…. Early identification of children at risk for renal scarring using the prediction rules developed in this study could help clinicians deliver specific treatment and follow-up for this small subgroup in the future,” the researchers concluded.
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Ellen R. Wald, MD
Urinary tract infection (UTI) is the most common serious bacterial infection in young children. This report by Shaikh and colleagues is an important study designed to inform the primary care provider regarding the risk of renal scarring in children of any age who experience their first UTI. The authors developed a simple predictive model using basic clinical, laboratory (microbiologic results of urine culture) and ultrasonographic data. In this model, a temperature ≥39°C earns 1 point, an organism other than Escherichia coli earns 1 point and an abnormal renal ultrasound (RUS) earns 2 points. A score of 2 or greater (present in 21.7 % of children) predicts renal scarring in 30.7% (about twice the baseline risk). This simple model does not require the performance of either blood tests (thereby avoiding venipuncture) or a voiding cystourethrogram.
RUSs performed on children aged 2 and 24 months experiencing their first febrile UTI can be expected to be abnormal in 12% to 15% of children. Most of these abnormalities are not “actionable,” ie, do not require an intervention (eg, double collecting system, calculus). Unfortunately, there were no data in this study on the precise nature of the abnormalities found on RUS. It is quite likely, that some findings (the 1% to 3% of actionable [eg, moderate hydronephrosis] findings) are much more predictive of renal scarring than others.
In the meanwhile, children with temperature ≥39°C and an organism other than E. coli, or those with “actionable” finds on RUS should be considered at high risk of renal scarring. When children are at high risk, it is critical to do close follow-up to insure comprehensive evaluation of all unexplained fevers so as to favor early detection of recurrent UTI.
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