The relationship between bladder debris on ultrasonography and urine analysis anomalies and culture positivity in children: a large-scale retrospective cohort study

Urinary tract ultrasound (UTUS) often detects bladder debris in children, but its clinical usefulness in evaluating children for a urinary tract infection (UTI) is unclear. Current pediatric studies evaluating this ultrasound finding are small, vary in design, and have not determined whether bladder debris adds diagnostic value beyond standard urinalysis. We assessed the clinical relevance of bladder debris in the largest pediatric cohort with paired urine culture. In this single-center retrospective cohort study (tertiary training and research hospital, January 2015–December 2024), we identified 9,083 patients with UTUS and urinalysis obtained within ± 7 days (primary cohort); 6,413 of these also had a valid paired urine culture. A same-day subgroup with valid culture ( n = 6,000) was used for multivariable modeling and decision curve analysis. We first tested whether debris independently predicted culture positivity beyond urinalysis, comparing a urinalysis-only model with one adding debris (logistic regression; ΔAUC; integrated discrimination improvement, IDI; continuous net reclassification improvement, NRI; decision curve analysis). We then asked a separate, practice-oriented question: when debris is found incidentally, does it justify reflex urinalysis? For this we compared the probability of any positive infection marker (pyuria, nitrite, or leukocyte esterase) in debris-positive versus debris-negative patients. Debris was present in 20.2% (1,831/9,083) of patients and was strongly associated with culture positivity on unadjusted analysis (OR 2.81, 95% CI 2.46–3.22), though as a stand-alone test it had high specificity (83.9–84.3%) but low sensitivity (33.6–35.0%). After adjusting for urinalysis parameters, this association weakened (adjusted OR 1.39, 95% CI 1.12–1.72), and adding debris to the urinalysis-based model gave essentially no gain in discrimination (ΔAUC 0.001, P = 0.143; IDI 0.0011, P = 0.076) or net clinical benefit (decision-curve differences within ± 0.003 across the 10–30% threshold range). Reclassification analysis showed a mixed picture: while overall NRI was significant (0.357), debris shifted risk estimates favorably for uninfected patients (NRI non-events + 0.686) but unfavorably for infected patients (NRI events − 0.328), indicating no consistent clinical advantage. In contrast, patients with incidental debris had a much higher probability of any positive infection marker than those without (44.6%( 817/1,1831) vs. 24.2%( 1,1755/7,252); OR 2.53, 95% CI 2.27–2.81). Bladder debris does not improve diagnostic models that already include urinalysis. However, in patients where urinalysis has not yet been obtained, incidentally detected bladder debris was associated with an approximately twofold higher probability of an abnormal urinalysis, which may support considering urinalysis in this setting. Incorporating this dual-perspective framework into pediatric clinical decision support may help avoid both excessive workup and missed indications.