Interstitial Fibrosis and Tubular Atrophy in IgA Nephropathy and Their Association With Renal Doppler Indices: A Prospective Observational Study

Background Interstitial fibrosis and tubular atrophy (IFTA) are major determinants of prognosis in IgA nephropathy (IgAn). This study evaluates the association of Doppler-derived renal resistive index (RRI) and atrophic index (AI) with IFTA and their ability to predict renal function decline in IgAN. Materials and Methods This prospective observational study included 50 patients with biopsy-proven IgAN evaluated between June 2023 and December 2024 at a tertiary care hospital. Pre-biopsy renal doppler ultrasonography was used to assess RRI and AI. IFTA was graded using the Oxford MEST-C classification, and renal function was followed quarterly for one year using eGFR. Associations and predictive performance were analyzed using appropriate statistical methods. Results The mean age was 40 years (male: female ratio 1.08:1). Hypertension, proteinuria, and renal dysfunction were present in 92, 92, and 88%, respectively. IFTA >25% was observed in 72% and was significantly associated with renal dysfunction ( p <0.001) and pre-existing hypertension ( p = 0.009). Neither arcuate nor interlobar RRI, nor AI, correlated with IFTA (all p >0.05). During follow-up, 40% had ≥50% eGFR decline and 20% progressed to end-stage kidney disease. Higher interlobar RRI ( p = 0.004) and mean composite RRI ( p = 0.001) predicted renal function decline, with composite RRI outperforming AI (AUC 0.767, 95% CI 0.635–0.899, p = 0.002 vs. AUC 0.687, 95% CI 0.538–0.835, p = 0.027; cut-off ≥0.62, sensitivity 100%, accuracy 72%). Conclusion Renal Doppler indices do not reliably reflect histological fibrosis in IgAN; however, elevated interlobar and composite RRI independently predict renal function decline. Their value as practical, non-invasive prognostic markers complementing clinical assessment needs confirmation.