Routine Doppler Ultrasonography Does Not Differentiate Acute Tubular Necrosis and Rejection in Early Pediatric Kidney Transplantation.

Introduction: Differentiating acute tubular necrosis (ATN) from rejection in pediatric kidney transplant (KT) recipients remains challenging and necessitates invasive biopsy. Doppler ultrasound-derived resistive index (RI) is a noninvasive modality to assess graft status, but its diagnostic utility in children is unclear. This study evaluates RI's ability to distinguish ATN and rejection in KT.

Methods: In this retrospective cohort (2000-2021), 296 pediatric KT recipients with surveillance or clinically indicated biopsies were categorized into uncomplicated (n = 164), ATN (n = 65), or rejection (n = 67) groups. RI was measured at 24 h, 3, 6, and 12 months post-KT. Linear mixed-effects models assessed temporal trends and associations with complications.

Results: Baseline demographics were similar between groups (p > 0.05), but significant differences were observed in cold ischemia time (p = 0.019), time to complication (p < 0.001), and lower graft function in complicated groups (p < 0.001 and p = 0.002). Median RI did not differ between groups in surveillance (p > 0.05) or clinically indicated biopsies (p > 0.05). Established RI thresholds of 0.7 and 0.8 lacked specificity (p > 0.05). In a multivariate model, RI increased temporally posttransplant (3 months: +0.04, p < 0.001; 1 year: +0.05, p < 0.001), inversely correlated with recipient age (p < 0.001), and marginally with donor kidney size (p = 0.009), but showed no association with complications (p > 0.05).

Conclusion: RI thresholds and trends do not differentiate ATN and rejection in pediatric KT. Temporal RI rise likely reflects systemic hemodynamic adaptation rather than pathology, limiting its standalone diagnostic utility. Future studies should integrate multimodal approaches with RI, clinical, and biochemical markers to refine noninvasive strategies.