Validation study of oxford classification of IgA nephropathy: the significance of extracapillary proliferation

Abstract

BACKGROUND AND OBJECTIVES The Oxford classification of IgA nephropathy (IgAN) includes mesangial hypercellularity, endocapillary hypercellularity, segmental glomerulosclerosis (S), and tubular atrophy/interstitial fibrosis (T) as prognosticators. The value of extracapillary proliferation (Ex) was not addressed. Because the Oxford classification excludes patients with urinary protein <0.5 g/d and eGFR <30 ml/min per 1.73 m(2) at biopsy, the significance of Ex should be confirmed by validation cohorts that include more rapidly progressive cases. We present such a study.

Design, setting, participants, & measurements: The significance of pathologic features for development end-stage renal failure (ESRF) was examined by multivariate analysis in 702 patients with IgAN. The association of Ex with kidney survival was examined by univariate analysis in 416 patients who met the Oxford criteria and 286 who did not, separately.

Results: In a multivariate model, S and T were significantly associated with ESRF. With addition of Ex, not S but Ex was significant for ESRF. In univariate analysis, kidney survival was significantly lower in patients with Ex than in those without, in patients who did not meet the Oxford criteria, but such a difference was not found in patients who met it.

Conclusions: The prognostic significance of Ex was evident in our cohort. It seems that Ex did not emerge from the Oxford classification as a prognosticator because of exclusion of severe cases (eGFR <30 ml/min per 1.73 m(2)). We suggest that extracapillary proliferation be included in the next version of the Oxford classification of IgAN to widen the scope of the classification.

Figure 1.

Kidney survival curve in patients with and without extracapillary proliferation. Kidney survival was significantly lower in patients with extracapillary proliferation than in those without it (P < 0.01). The number of patients remaining at 60, 120, 180, and 240 months of follow-up are shown at the bottom.

Figure 2.

Kidney survival curve in patients with and without extracapillary proliferation in the patients who met inclusion criteria of the Oxford classification. The inclusion criteria of Oxford classification is UP-UCR >0.5 and eGFR >30 ml/min per 1.73 m² at the time of renal biopsy and followed up at least 12 months. There was no statistical significant difference in kidney survival between the patients with extracapillary proliferation and those without it. The number of patients remaining at 60, 120, 180, and 240 months of follow-up are shown at the bottom.

Figure 3.

Kidney survival curve in patients with and without extracapillary proliferation in the patients who did not meet inclusion criteria of the Oxford classification. The patients who did not meet inclusion criteria of Oxford classification had a UP-UCR <0.5 or eGFR <30 ml/min per 1.73 m² at the time of renal biopsy or follow-up period was <12 months. Kidney survival of patients with extracapillary proliferation was significantly lower than those without it (P < 0.01). The kidney survival rapidly declined within 5 years from the biopsy in patients with extracapillary proliferation. The number of patients remaining at 60, 120, 180, and 240 months of follow-up are shown at the bottom.