Announcer:
You’re listening to Clinician’s Roundtable on ReachMD. On this episode, we’ll hear from Dr. John Sim, who’s a nephrologist at Kaiser Permanente Los Angeles Medical Center and a clinician investigator at the Kaiser Permanente Southern California Department of Research and Evaluation. He’ll be sharing findings from a study investigating the incidence of IgA nephropathy across different racial and ethnic groups. Here’s Dr. Sim now.
Dr. Sim:
We wanted to determine the incidence of IgA nephropathy within our health system, and we also tried to get a better understanding of IgA nephropathy incidence within the United States. So that’s given the fact that IgA nephropathy is a rare disease and also given the fact that efforts to study rates of IgA nephropathy in the United States have been limited in a few ways. We don’t have a national registry for glomerular diseases or kidney biopsies, so we’ve always had to rely on more fragmented and limited data to get an estimate of IgA nephropathy incidence in the United States, and some of our previous estimates have been based on small homogeneous populations and are focused on specific geographic areas of our large diverse country. And sometimes we’ve used claims information to study IgA nephropathy rates, and we know that could be less precise since IgA nephropathy is a kidney biopsy-proven diagnosis. So without a national health system or health database, we wanted to see if we could use a large sample from the racially ethnically diverse population that is Southern California to try to determine the incidence of IgA nephropathy overall and to determine incidence by specific race groups, including Asians, Blacks, Hispanics, and Whites and then estimate a single standardized incidence rate for the United States.
So our study was performed within Kaiser Permanente Southern California, and we used a membership population of Kaiser Permanente Southern California, which is a very diverse population of over 4.8 million members. That mirrors California in a lot of ways. So during the period 2010 to 2021, incident IgA nephropathy patients were identified at the time of their kidney biopsy, and what we did with that was we reported overall incidence rates as cases per 100,000 patient years. Then, we reported incidence rate separately by different race/ethnic groups. And finally, we estimated a single standardized incidence rate using the 2020 US Census data.
In the 12-year period, the overall annual incidence rate of IgA nephropathy was about 1.7 cases per 100,000 patient years. But there were differences by race and ethnicity, with the highest being among Asians and Pacific Islander patients at 4.5 patient years, and it was lowest among Black patients at 0.6. White patients had an incidence about 1.2, while Hispanic patients, who generally have not been well studied among IgA nephropathy patients, had an incidence of 1.7, so somewhere between Asians and Whites. Overall, when we standardized for 2020 US Census, the annual incidence rate was estimated about 1.4 cases per 100,000 patient years. Finally, we also observed that IgA nephropathy patients were biopsy diagnosed at relatively advanced CKD. And what I mean by that is that the median EGFR of our cohort was 51 or CKD stage 3, and the median level of proteinuria at biopsy was 1.8g.
So I think that our estimated incidence is actually probably lower than the actual incidence because of our historical approach toward IgA nephropathy patients where we have a higher threshold for performing kidney biopsies. And we just assumed that patients have IgA nephropathy, especially those patients with milder presentation in terms of their level of proteinuria or if they have intact or near normal kidney function.
Announcer:
That was Dr. John Sim talking about the incidence of IgA nephropathy across different racial and ethnic groups. To access this and other episodes in our series, visit Clinician’s Roundtable on ReachMD.com, where you can Be Part of the Knowledge. Thanks for listening!
