Validation study of Oxford Classification of IgA Nephropathy: the significance of extracapillary hypercellularity and mesangial IgG immunostaining

The Oxford classification (OC) of IgA Nephropathy (IgAN) identified mesangial hypercellularity (M), endocapillary hypercellularity (E), segmental glomerulosclerosis (S), and tubular atrophy/interstitial fibrosis (T) as predictors of outcome. We aimed to validate the OC and to investigate the clinical significance of extracapillary hypercellularity and IgG immunostaining. We examined the renal outcome at December 31, 2014, of 121 adult patients with biopsy proven primary IgAN between 2003 and 2013. The primary endpoint was doubling of serum creatinine or renal replacement therapy initiation. The mean observation period was 59.7 months. Thirty-one percent of the patients presented with a grade of extracapillary hypercellularity. In comparison with the group with no crescents, they had higher grade of inflammation, lower eGFR and increased proteinuria. There were no differences between the IgA and IgA&IgG immunostaining groups regarding the disease progression risk factors. Mean kidney survival time for the entire cohort was 10.6 (9.1, 12.0) years. In the Cox regression model, the independent predictors of decreased renal survival were eGFR at time of biopsy, S1 and the presence of crescents. Our study showed that extracapillary proliferation and S1 had the greatest importance in establishing the renal prognosis of patients with IgAN.