#260 Epidemiology of immunoglobulin A nephropathy (IgAN) in Germany
Authors: Roll Matthias , Gladbach Amadeus , Selinger Isabella , Hardt Thomas , Himmelhaus Helena , Jacob Christian , Stremel Timotheus , Theil Julia , Floege Jürgen 
Published: May 2024

Abstract

Background and Aims
Immunoglobulin A nephropathy (IgAN) is a rare kidney disease characterized by proteinuria, persistent micro- or macrohematuria, and arterial hypertension. It can take a variety of courses from long-term minor symptoms to rapid progressive loss of kidney function with terminal renal failure. Epidemiological measures often refer to the proportion of IgAN among patients with glomerulonephritis instead of the entire population. Therefore, we estimated the prevalence and incidence of IgAN in Germany.

Method
Statutory health insurance (SHI) claims data from a large German database (InGef research database) with approximately four million insurees was retrospectively analyzed. The database represents about 5% of the German population and is representative of the German demographic and clinical structure in terms of age, gender, region, morbidity, mortality, and medication usage.
As there is no specific IgAN code in ICD-10-GM and coding practices vary between physicians, two algorithms with different sets of codes were developed to estimate a lower and upper bound of the 1-year prevalence and incidence from 2017-2022. The lower bound considered specific diagnosis codes which usually rely on biopsies (N00.3, N02.3, N06.3). The upper bound included a broader field of specific and unspecific codes (N00.3, N02.3, N02.5, N02.7, N02.8, N02.9, N06.3, N06.8) that are potentially used by physicians to diagnose IgAN. Identified patients were described in terms of age and gender. Results were extrapolated to the German overall population, and a trend for the upcoming five years was estimated by applying the mean prevalence and incidence from the years 2017 to 2022 to the forecasted German population for the years 2023 to 2027.

Results
In 2022, the 1-year prevalence of IgAN ranged from 5 (lower bound) to 38 (upper bound) per 100 000 individuals in Germany. This corresponds to approximately 4 000 and 32 200 affected patients in Germany, respectively. There was no significant change from 2017 to 2022 with mean rates ranging from 4 (lower bound) to 38 (upper bound) per 100 000 individuals in Germany. The number of prevalent patients in Germany is expected to slowly increase in the coming years due to a forecasted increasing German overall population. About 57% of the prevalent IgAN patients in 2022 were male and the mean age was 59 years for the upper bound. For the lower bound about 73% of the prevalent IgAN patients in 2022 were male and the mean age was 53.
The 1-year incidence of IgAN in 2022 ranged from 0.2 (lower bound) to 0.6 (upper bound) per 100 000 individuals in Germany. Extrapolation to the German population resulted in 164 to 538 newly diagnosed IgAN patients, respectively. Both the lower and the upper bound remained stable from 2017 to 2022 with slight fluctuations and a mean incidence rate of 0.2 (lower bound) and 0.6 (upper bound) per 100 000. The trend estimation showed steady numbers of incident patients in Germany until 2027 with a minor tendency towards an increase. About 86% (lower bound) and 83% (upper bound) of the incident IgAN patients in 2022 were male and the mean age was 36 years (lower bound) and 44 years (upper bound).

Conclusion
Estimating the epidemiology of IgAN is challenging as physicians use different ICD codes for diagnosis. To capture the uncertainty, an upper and lower bound of the prevalence and incidence were assessed as a minimum and maximum of patient numbers. Overall, IgAN was shown to be a rare disease with a prevalence of less than 50 per 100 000 in Germany. The upper bound of the incidence rate dropped in 2020 which may be associated with the onset of the global COVID-19 pandemic in March 2020, but the rate picked up in 2021 and the lower bound did not indicate an effect caused by the pandemic. Due to the forecasted rising population in Germany until 2027, the total number of prevalent and incident IgAN patient is expected to increase slowly.