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

Abstract

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. 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. 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%). 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.