External validation of the Oxford classification of IgA nephropathy: A retrospective study of 70 patients from Saudi Arabia

Abstract

The validity of the Oxford classification of immunoglobulin (Ig)A nephropathy has not been fully explored in the Arab population. The aim of this study was to assess the validity of this classification in a cohort of adult Saudi patients with histologically proven IgA nephropathy. A retrospective review of clinical and histological data of patients with biopsy-proven IgA nephropathy diagnosed between May 1998 and May 2011 was undertaken. The study was conducted at two institutions in Riyadh, Saudi Arabia. A total of 70 patients (46% females) with primary IgA nephropathy were included, with a mean age of 32.2 ± 12.9 years. The median follow-up was 3.5 years. The primary endpoint was decreased renal function, which was defined as 50% decrease in estimated glomerular filtration rate from baseline at last follow up. Higher mesangial score and later stage of segmental glomerulosclerosis showed trends towards correlations with a higher degree of proteinuria and lower estimated glomerular filtration rate at presentation and a higher rate of worsening of renal function, but these trends did not reach statistical significance ( p > 0.05). However, endocapillary hypercellularity and tubular atrophy/interstitial fibrosis were significantly associated with reduced initial estimated glomerular filtration rate and higher initial proteinuria. In multivariate logistic regression, the worsening of renal function was not predicted by any histologic class. The Oxford classification system is a useful tool that reflects the severity of the initial clinical presentation in Arabs with IgA nephropathy. However, it did not predict long-term renal outcomes. 在阿拉伯人群中，IgA 腎病變的牛津分類法尚未通過充分的驗證。本研究以經過組織學驗證為 IgA 腎病變的沙烏地阿拉伯成年患者為對象，對此分類法的效度進行了評估。 是次分析所涉及的個案，是從 1998 年 5 月至 2011 年 5 月間，經切片證實為原發性 IgA 腎病變的 70 位患者，女性佔 46%，平均年齡 32.2 ± 12.9 歲，均來自沙烏地阿拉伯利雅得的兩家院所。追蹤期間中位數為 3.5 年，首要終點為腎功能下降，其定義為腎小球濾過速率 (GFR) 估算值降幅達 50% (相對於基線)。 分析顯示，環間膜評分偏高、與較晚期節段性腎小球硬化症，均與以下呈現相關的傾向：基線較嚴重的蛋白尿、基線較低的 GFR 估算值、及追蹤期間較明顯的腎功能惡化，雖然未達統計學意義 ( p > 0.05)。然而，微血管內細胞過多、及腎小管萎縮/間質纖維化，則與基線較嚴重的蛋白尿、及基線較低的 GFR 估算值呈明顯關聯。在多變項邏輯迴歸分析中，組織學分類並未能預測腎功能惡化的發生。 對於阿拉伯的 IgA 腎病變成年患者，牛津分類法可有效反映初期的病情嚴重性，但未能預測腎功能的長期變化。