Background and purpose of the study: Urinary tract dilatation (UTD) is the most common genitourinary abnormality detected in routine prenatal ultrasound (US) examinations. Some UTDs can lead to kidney damage, which is the primary cause of chronic renal disease in children, so a timely diagnosis and treatment are mandatory. The currently most investigated and promising biomarker is neutrophil gelatinase-associated lipocalin in urine (uNGAL), which is of special importance in the neonatal population due to its non-invasive urine collection. The aim of our study was to evaluate its role in newborns with congenital unilateral UTD. US of the urinary tract, though, remains the first and safest investigation needed for the evaluation of fetuses and newborns with suspected UTD. We evaluated the ultrasound UTD A (antenatal)/P (postnatal) classification system, which has been in use since 2014, and its association with specific uropathies and different clinical outcomes.
Patients and methods: In the first, prospective part of the study, we enrolled 38 term newborns with congenital unilateral UTD, while 38 healthy term newborns represented the control group. US of the urinary tract was done according to the UTD P classification system, and the uNGAL concentration was measured by chemiluminescence analysis. Some of the newborns needed additional workup to define the etiology of the congenital kidney disease (cystograms, scintigraphies, urography). The newborns in the study group were further divided into 2 subgroups regarding the urinary tract obstruction, and subsequently according to the need for surgical or conservative treatment. In the retrospective part of our study, we enrolled 126 newborns with unilateral UTD and 40 newborns with bilateral UTD. Data was obtained on UTD A and UTD P grades, as well as clinical events such as specific uropathies, urinary tract infections, the need for prophylactic antibiotic therapy or surgical intervention, the rate and timing of spontaneous resolution, and renal function outcome at the end of follow-up.
Results: Our prospective study showed significantly higher uNGAL values in the study subgroup with urinary tract obstruction compared to the control group (median 15.9 (IQR 6.4-25.0) vs median 5.7 (IQR 3.6-11.1), Kruskal-Wallis test, p = 0.016). A receiver operating curve (ROC) analysis was performed to determine the diagnostic profile of uNGAL to detect newborns with urinary tract obstruction. The analysis showed sensitivity to be 89 % and specificity 51 % at the cut-off point of uNGAL 5.5 μg/L. The area under the curve (AUC) was 0.72 (95 % CI 0.59⠒0.85). Our retrospective study showed a statistically significant association of UTD A 2-3 with UTD P 2 or 3 (sensitivity 88 %, specificity 32 %, p < 0.005). We have also proven a statistically significant association between different UTD P grades and specific clinical outcomes: specific uropathies (reflux, obstructive, idiopathic) (χ2 test, p < 0.001), urinary tract infections rate (χ2 test, p = 0.003), antibiotic prophylactic treatment (χ2 test, p < 0.001), the need for surgical procedure (χ2 test, p < 0.001), spontaneous resolution rate (χ2 test, p < 0.001), and time to spontaneous resolution (log-rank test, p = 0.011). We did not find any association with renal function at the end of follow-up, as all our patients had normal renal function at the end of follow-up (the median follow-up time was 24 months (IQR 12⠒48)).
Conclusions: The prospective part of our study confirmed the potential usefulness of uNGAL from a single urine sample in the first few days of life as a non-invasive marker of kidney injury in newborns with congenital unilateral UTD. In the second, retrospective part of our study, we confirmed the validity and utility of the UTD A/P classification system in
predicting different clinical outcomes in newborns with congenital unilateral or bilateral UTD.
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