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: A cross-sectional study between January 1, 2010, and December 31, 2021 within Kaiser Permanente Southern California was performed. Patients (age >/=18 years) who underwent a native kidney biopsy and identified as having primary IgAN comprised the study population. Laboratory, demographic, and comorbidity information were obtained from the 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 were 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 Islander (4.5) and Hispanic (1.7) patients and lowest among White (1.2) and Black (0.6) patients. Median estimated glomerular filtration rate (eGFR) was 51 mL/min with median urine protein creatinine ratio (uPCR) 1.8 g/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 kidney function and proteinuria at biopsy.