Racial, Ethnic IgA Nephropathy Stratification Provides New Insight Into US Incidence

John Sim, MD

Credit: Kaiser Permanente

New research is providing an overview of racially and ethnically stratified IgA nephropathy (IgAN) incidence rates in the United States, addressing the previous underrepresentation of certain groups in prior studies.¹

Results suggest an estimated annual incidence of 1.4 cases per 100,000 person-years during the 12-year study period, with the greatest incidence rates observed among Asian/Pacific Islander and Hispanic patients.¹

A leading cause of glomerulonephritis and renal failure, IgAN typically progresses gradually, but estimates project between 20% and 50% of affected patients develop end-stage renal disease within 20 years of diagnosis. The clinical course of IgAN varies from patient to patient, underscoring the importance of prompt diagnosis and disease management. Understanding factors facilitating targeted interventions could aid this process.²

“Prior studies in the United States have been conducted in areas that were predominantly White and therefore under-represented other racial/ethnic groups. Given the variability of incidence by race and ethnicity in IgAN, examining data from diverse populations would help in estimating incidence for a multiracial/multiethnic country such as the US,” John Sim, MD, a nephrologist and clinical researcher at the Kaiser Permanente Los Angeles Medical Center and a clinical professor at Kaiser Permanente Bernard J. Tyson School of Medicine, and colleagues wrote.¹ “Our study is one of the few to report data on a large IgAN cohort across different racial/ethnic groups (including Hispanic/Latino individuals) that was biopsy confirmed.”

To address shortcomings of prior research, investigators conducted a cross-sectional study using a racially, ethnically, and socioeconomically diverse cohort within Kaiser Permanente Southern California, a large integrated health system with > 4.8 million members. Patients ≥ 18 years of age who underwent a native kidney biopsy between January 1, 2010, and December 31, 2021, and were diagnosed with primary IgAN were included in the study.¹

Investigators obtained laboratory, demographic, and co-morbidity information from electronic health records. They calculated annual incidence rates for biopsy-proved IgAN per 100,000 person-years and standardized them to 2020 US Census data.¹

Of 9392 individuals who underwent kidney biopsy during the study period, 606 adult patients were diagnosed with primary IgAN. Among this group, the mean age was 46 years and 51.2% of patients were male. The median estimated glomerular filtration rate (eGFR) at biopsy was 51 ml/min/1.73 m2, 18.8% of patients had eGFR <30 ml/min/1.73 m2, and the median urine protein creatinine ratio (UPCR) was 1.8 g/g.¹

Investigators noted the racial/ethnic composition of the cohort was 30.4% Asian/Pacific Islander; 3.1% Black; 38.6% Hispanic/Latino; 25.6% White; and 2.3% other/unknown.¹

Upon analysis, the crude annual IgAN incidence rates ranged from 1.3 per 100,000 person-years during 2016-2020 to 2.2 per 100,000 person-years in 2012. Investigators called attention to a slight downward trend in incidence over the study duration (Mann-Kendall trend test: Kendall's τ = –0.45; P = .04).¹

The US Census standardized incidence rate of IgAN was 1.4 per 100,000 person-years during the 12-year period. The adjusted annual incidence rates ranged from 1.0 per 100,000 person-years in 2018 to 1.8 per 100,000 person-years in 2010 and 2012.¹

Of note, the incidence rate was greatest among Asian/Pacific Islander patients (4.5 per 100,000 person-years) and Hispanic patients (1.7 per 100,000 person-years) but was lowest among White patients (1.2 per 100,000 person-years) and Black patients (0.6 per 100,000 person-years).¹

Investigators acknowledged multiple limitations to these findings, including the potential lack of generalizability to the entire United States; differences in environmental risk factors relative to areas outside of Southern California; and oversampling of individuals proactively seeking health care screenings that would lead to biopsy.¹

“Our study provides racially and ethnically stratified IgAN incidence rates from a large and diverse US population, including under-researched subgroups such as Hispanic/Latino patients. These data might be used to inform targeted interventions for achieving earlier IgAN diagnosis,” investigators concluded.¹

References

1. ^{Sim JJ, Chen Q, Cannizzaro N, et al. Incidence of Adult Primary Immunoglobulin A Nephropathy Among a Racially/Ethnically Diverse Population in the United States. Am J Nephrol. https://doi.org/10.1159/000541869}
2. ^{Rout P, Limaiem F, Hashmi MF. IgA Nephropathy (Berger Disease). StatPearls. April 22, 2024. Accessed November 7, 2024. https://www.ncbi.nlm.nih.gov/books/NBK538214/}