The Association of the Oxford Classification Score with Longitudinal Estimated Glomerular Filtration Rate Decline in Patients with Immunoglobulin A Nephropathy: A Mixed-Method Study

INTRODUCTION: The Oxford Classification score, which predicts renal outcomes for immunoglobulin A nephropathy (IgAN), is widely used in clinical practice. Nevertheless, the relationship between these markers and longitudinal changes in renal function are poorly understood. METHODS: This was a population-based retrospective cohort study of 280 adults with biopsy-proven primary IgAN from 2011 to 2018. We used generalized additive mixed models to control for traditional kidney disease risk factors to analyze the associations between Oxford Classification MEST-C scores (mesangial hypercellularity, M; endocapillary hypercellularity, E; segmental glomerulosclerosis, S; tubular atrophy/interstitial fibrosis, T; crescents, C) and longitudinal changes in the estimated glomerular filtration rate (eGFR) after renal biopsy. RESULTS: The median eGFR was 78.2 mL/min/1.73 m(2) at baseline, and then it decreased on average by 1.3 mL/min/1.73 m(2) per year in the entire cohort. In adjusted models, compared with patients without relative lesions, the presence of T > 50% (T2) (−5.7; 95% confidence interval [CI], −9.5 to −2.0 mL/min/1.73m(2) per year) was associated with the fastest eGFR decline. S present (S1) (−2.9; 95% CI, −4.6 to −1.1 mL/min/1.73m(2) per year) and C > 25% glomeruli (C2) (−3.4; 95% CI, −6.4 to −0.5 mL/min/1.73m(2) per year) also demonstrated steeper eGFR declines. However, we found no association between M > 0.5 (M1), E present (E1), T 26%–50% (T1), and C present ≥ 1 glomerulus (C1), and progressive eGFR decline (p > 0.05). CONCLUSION: The Oxford Classification scores, S1, T2, and C2, were independently associated with the longitudinal decreases in renal function in patients with IgAN. These findings suggested therapies targeted at improving early damage to these lesions might be essential to delay renal progression.