Incidence of Adult Primary Immunoglobulin A Nephropathy Among a Racially/Ethnically Diverse Population in the United States.

Introduction: IgA nephropathy (IgAN), a leading cause of kidney failure worldwide, is one of the most common forms of primary glomerulonephropathy with variability by race and ethnicity. Using a diverse cohort within a large integrated health system in the United States (US), we identified and characterized patients with biopsy-proven IgAN and report annual incidence rates across racial/ethnic groups and standardized to the US nationally.

Methods: Cross sectional study between 1/1/2010 through 12/31/2021 within Kaiser Permanente Southern California was performed. Patients (age>/=18years) who underwent a native kidney biopsy and identified as primary IgAN comprised the study population. Laboratory, demographic, and co morbidity information obtained from electronic health records. Annual incidence rates were calculated for biopsy-proven IgAN (per 100,000 person-years) and standardized to 2020 US Census.

Results: Of 9,392 individuals who underwent kidney biopsy, 606 adult patients identified with primary IgAN. Crude annual IgAN incidence rates ranged from 1.3 to 2.2 (per 100,000 person years). US census standardized incidence rate (CI) of IgAN was 1.4 (0.8, 2.0) per 100,000 person years in the 12-year period. Incidence rate (per 100,000 person years) was highest among Asian/Pacific Islanders (4.5) and Hispanics (1.7) and lowest among Whites (1.2) and Blacks (0.6). Median eGFR was 51 ml/min with median uPCR 1.8g/g.

Conclusion: Among a large diverse US population within Southern California, we observed an IgAN incidence rate of 1.7 which estimated to a standardized US incidence of 1.4 (per 100,000 person years) within a 12-year period. Patients appear to be diagnosed at more advanced disease given the eGFR and uPCR at biopsy.