#3242 Long-term outcomes in IgA nephropathy: findings from the ERKNet patient registry (ERKReg)

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Abstract Background and Aims In IgA nephropathy, kidney function gradually declines, but at a highly variable pace. A study of IgA nephropathy patients followed in the UK nationwide RaDaR registry recently depicted a generally poor long-term prognosis, with only few patients likely to avoid kidney failure during their lifetime. In this study, we explored the relationships of proteinuria and eGFR slope with the lifetime risk of kidney failure in patients followed in European reference centers and recorded in the European Rare Kidney Disease Registry (ERKReg). Method Data were analyzed on 31.12.2024. At that time, the IgA nephropathy cohort within ERKReg comprised 884 adults and 385 children from 10 European countries and 49 units, all with a biopsy-proven diagnosis of IgA nephropathy. Kidney failure was defined as the first occurrence of kidney replacement therapy (dialysis or transplant) or eGFR <15 mL/min/1.73 m². Kidney survival was analyzed from the time of diagnosis to kidney failure using Kaplan-Meier and Cox regression models. To compare the findings with those of the RaDaR study, a matched “RaDaR Inclusion subcohort” was created by including only patients with proteinuria >0.5 g/d or eGFR <60 ml/min/1.73 m² at any time. Results The median (interquartile range (iqr)) age at diagnosis for the total cohort was 33 (17, 49) years, the median age at first recorded centre visit 43.7 (24, 60) years and the median follow-up duration 6.0 (2.3, 14) years from diagnosis. During the observation period, 240 (18.9%) patients progressed to kidney failure and 7 (0.6%) died. The overall median kidney survival following diagnosis was 35.9 (95% CI: 29.0 to NE) years. For patients with manifestation at adult age, the median age at diagnosis was 41.8 (31, 57), median kidney survival time 35 years (95% CI: 27 to NE), and 10- and 20-year kidney survival rates 75.7% (71.9% to 79.1%) and 64.2% (59.0% to 68.8%) respectively. By comparison, disease manifestation during childhood was diagnosed at a median age of 13.2 (9, 16), with an estimated 10- and 20-year kidney survival of 86.7% (80.6% to 91.1%) and 79.1% (69.6% to 86.0%), respectively. Disease manifestation at adult age was independently associated with a higher risk for kidney failure as compared to disease manifestation during childhood, with an adjusted hazard ratio of 2.0 (95% CI: 1.4 to 2.8, P < 0.001) (Fig. 1). Time-averaged proteinuria was strongly associated with worse kidney survival, with about threefold higher risk for kidney failure in patients with 0.5–1.0 g/d time-averaged proteinuria compared to patients with <0.5 g/d (Table 1). The RaDaR Inclusion subcohort, consisting of patients with more severe disease, had a median kidney survival of 28.3 years (95% CI: 22.0 to 35.7). These outcomes were notably better than those reported in the RaDaR study, which showed an overall median survival of 11.4 years from diagnosis. Patient sex and the region of residence in Europe had no significant impact on kidney survival. Conclusion In this large European IgA nephropathy cohort, poorer kidney survival was associated with disease manifestation at adult age and greater time averaged proteinuria. Even mild proteinuria had a notable impact on kidney function prognosis. The outcomes observed in this registry cohort indicate a more favorable prognosis for most patients compared to the findings of the British RaDaR study.

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