IgA nephropathy occurrence, treatment, and prognosis in the last two decades in Denmark

Abstract Background and hypothesis IgA nephropathy (IgAN) is the leading cause of primary glomerulonephritis; however, reported incidences and prevalences vary substantially across countries. This study assessed the epidemiology of IgAN including changes in incidence, prevalence, treatment, and prognosis in Denmark during 2002–2023. Method This population-based cohort study included all adult patients with a biopsy-verified diagnosis of IgAN in Denmark during 22 years. Danish health registries with data on hospital diagnoses, pharmacological therapy, and laboratory results were used. The study period was divided into three calendar periods. Crude and age- and sex-standardized incidence rates and prevalences of IgAN in the Danish population were computed. The period specific five-year and the overall 15-year cumulative incidence (risk) of kidney failure with replacement therapy (KFRT) and of all-cause death (mortality) were estimated. Results The study population included 1 298 incident adult patients with IgAN. The overall incidence of IgAN was 13.1 per 1 000 000 person-years (95% CI 9.8–16.5). The annual incidence increased threefold during the study period. The prevalence reached 261 per 1 000 000 people in year 2023 (95% CI 246–275). Median eGFR was 60 ml/min/1.73 m2 (IQR 40–85) and median uACR was 1.2 g/g (IQR 0.6–2.2) at time of diagnosis. Following diagnosis, renin-angiotensin system inhibitors constituted a mainstay of treatment while corticosteroid use declined throughout the period. The 15-year risk of KFRT was 42.7% (95% CI 38.4–46.9). The 15-year all-cause mortality was 22.8% (95% CI 19.4–26.4). There were no substantial changes in the 5-year risk of KFRT or mortality during the study period. Conclusion The annual incidence of IgAN in Denmark increased during the study period. At the time of biopsy, many patients had preserved kidney function and substantial albuminuria. The risk of KFRT and mortality was substantial, and overall, the prognosis for Danish IgAN patients did not improve over the past two decades.