Long-term outcomes of patients with IgA nephropathy in the German CKD cohort.

Abstract

The importance of albuminuria as opposed to proteinuria in predicting kidney outcomes in primary immunoglobulin A nephropathy (IgAN) is not well established. From 2010 to 2012, 421 patients with biopsy-proven IgAN have been enrolled into the German Chronic Kidney Disease (GCKD) cohort, a prospective observational cohort study (N=5217). Adjudicated endpoints include a composite kidney endpoint (CKE) consisting of eGFR decline >40%, eGFR <15ml/min/1.73m2 and initiation of kidney replacement therapy; the individual components of the CKE; and combined major adverse cardiac events (MACE), including non-fatal myocardial infarction, non-fatal stroke and all-cause mortality. The associations between the incidence of CKE and baseline factors, including demographics, laboratory values and comorbidities were analysed using the Cox proportional hazards regression model. The mean age of IgAN patients at baseline was 51.6years (±13.6) and 67% were male. The patient-reported duration of disease at baseline was 5.9±8.1years. Baseline median urine albumin:creatinine ratio (UACR) was 0.4g/g [interquartile range (IQR) 0.1-0.8] and mean eGFR was 52.5±22.4ml/min/1.73m2. Over a follow-up of 6.5years, 64 (15.2%) patients experienced a >40% eGFR decline, 3 (0.7%) reached eGFR <15ml/min/1.73m2, 53 (12.6%) initiated kidney replacement therapy and 28% of the patients experienced the CKE. Albuminuria, with reference to <0.1g/g, was most associated with CKE. Hazard ratios (HRs) at UACRs of 0.1-0.6g/g, 0.6-1.4g/g, 1.4-2.2g/g and >2.2g/g were 2.03 [95% confidence interval (CI) 1.02-4.05], 3.8 (95% CI 1.92-7.5), 5.64 (95% CI 2.58-12.33) and 5.02 (95% CI 2.29-11-03), respectively. Regarding MACE, the presence of diabetes [HR 2.53 (95% CI 1.11-5.78)] was the most strongly associated factor, whereas UACR and eGFR did not show significant associations. In the GCKD IgAN subcohort, more than every fourth patient experienced a CKE event within 6.5years. Our findings support the use of albuminuria as a surrogate to assess the risk of poor kidney outcomes.