Validation of Oxford classification in IgA nephropathy with less advanced histology in a single center experience

Abstract

Background: Immunoglobulin A (IgA) nephropathy is the most common cause of primary glomerulonephritis in the world. Several grading systems including Haas and WHO classification have been used to categorize the pathological grades and predict the natural course of disease and were valuable to compare the renal outcomes in IgA nephropathy. However, the role of histological grading system to predict the renal outcomes in less advanced pathological stage except advanced or minimal lesions is still controversial. Oxford classification, new grading system in IgA nephropathy, is highly reproducible and has a predictive capacity of renal outcomes. The aim of the study was to assess the performance, Oxford classification on the prediction of prognosis in IgA nephropathy patients with less advanced renal pathology.Subjects and methods: We collected 319 kidney biopsy samples with Haas subclass II, III and IV and histologically and reclassified according to Oxford classification. Based on medical records, demographic and clinical data were reviewed retrospectively. Study end point was time to a doubling of the baseline serum creatinine levels or end stage renal disease (ESRD). The slope of decline of GFR over time was calculated by linear regression analysis of serial eGFR measurement for each patient. Results: The mean age of study subjects was 33 years, and 56% were female. Of the subjects, 127 patients were taking antihypertensive medication and 12 patients were treated with immunosuppressive agents at the time of renal biopsy. Baseline eGFR and the amount of proteinuria were 89.4±31.7 ml/min/1.73m2 and 1.44±1.66 g/day, respectively. The amount of proteinuria and baseline GFR were significantly associated with mesangial hypercellularity and tubule-interstitial lesions in details of Oxford classification. In the multivariate linear regression analysis, the decline slope of GFR was associated with mesangial hypercellularity, tubule-interstitial lesions, baseline GFR and the amount of proteinuria. During the follow up period, 38 (11.9%) subjects were reached to the primary end point. There were no significant differences in renal survival rate according to Haas subclass in this study. However, tubule-interstitial lesion by Oxford classification was a significant risk factor for renal survival after adjustment of demographic data, amount of proteinuria, baseline GFR, and hypertension (p<0.05).Conclusion:This study demonstrates that Oxford classification is valuable to predict the renal outcome in IgA nephropathy patients with less advanced histology.