Long term outcomes of patients with IgA nephropathy in the German CKD (GCKD) cohort

Background and Aims The importance of albuminuria as opposed to proteinuria in predicting kidney outcomes in primary IgA nephropathy (IgAN) is not well established. Method 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 included a Composite Kidney Endpoint (CKE) consisting of eGFR decline > 40%, eGFR < 15 ml/min/1.73 m2 and initiation of kidney replacement therapy; the individual components of the CKE; and combined major adverse cardiac events (MACE), including nonfatal myocardial infarction, nonfatal stroke, and all-cause mortality. The associations between the incidence of CKE and baseline factors, including demographics, laboratory values and comorbidities were analyzed using the Cox proportional hazards regression model. Results The mean age at baseline of IgAN patients was 51.6 years (± 13.6) and 67% were male. Patient-reported duration of disease at baseline was 5.9 ± 8.1 years. Baseline median UACR was 0.4 g/g (0.1–0.8) and mean eGFR was 52.5 ± 22.4 mL/min/1.73m2. Over a follow-up of 6.5 years, 64 (15.2%) experienced > 40% eGFR decline, 3 (0.7%) reached eGFR < 15 ml/min and 53 (12.6%) initiated kidney replacement therapy and 28% of the patients experienced the CKE. Albuminuria, with reference to < 0.1 g/g was most associated with CKE. Hazard ratios (95% CI) at UACR 0.1–0.6 g/g, 0.6–1.4 g/g, 1.4–2.2 g/g and > 2.2 g/g were 2.03 (1.02–4.05), 3.8 (1.92–7.5), 5.64 (2.58–12.33) and 5.02 (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. Conclusion In the GCKD IgAN sub-cohort more than every fourth patient experienced a CKE event within 6.5 years. Our findings support the use of albuminuria as a surrogate to assess the risk of poor kidney outcomes.