Oxford classification of immunoglobulin A nephropathy: an update

This review summarizes the recommendations for reporting immunoglobulin A (IgA) nephropathy biopsies and their evidence base, discusses the limitations of the Oxford Classification study and presents the findings of recent validation studies.

The Oxford Classification identified four histological lesions as independent prognostic factors: mesangial hypercellularity (M), endocapillary hypercellularity (E), segmental glomerulosclerosis (S) and tubular atrophy/interstitial fibrosis (T). The MEST criteria predicted outcome in some, but not all, of 13 recent validation studies. M is of independent prognostic value in four out of 13 studies, S in four out of 13 and T in 10 out of 13. Apparently contradictory findings reflect differences in patient selection criteria, treatment and outcome measures. The Oxford Classification study provided indirect evidence that endocapillary hypercellularity is responsive to immunosuppressive therapy. This is confirmed in two validation studies. One study, which included patients with rapidly progressive disease, found glomerular crescents to be a significant prognostic marker. Immunohistological findings correlate with proliferative glomerular lesions but are not of independent prognostic value.

The Oxford Classification is applicable to patients who were excluded from the original cohort, including those with rapidly progressive disease, and the prognostic value of proliferative glomerular lesions is influenced by immunosuppressive therapy. The Oxford schema will be reviewed in the light of recent findings.