Lower Income Linked to Increased Risk of Lupus Nephritis, New Study Finds

Lower income is associated with a significantly higher risk of certain kidney diseases, including lupus nephritis, a new study found.

The study, “Socioeconomic Position and Incidence of Glomerular Diseases,” was published in the Clinical Journal of American Society of Nephrology.

How much money individuals have can have a direct impact on their health, as it can affect everything from access to healthcare, lifestyle, and stress levels. However, the impact of income status on glomerular diseases – disorders affecting the glomeruli, or structures in the kidney that filter blood – has not been thoroughly assessed.

To learn more, a team of researchers now used clinical databases to identify people with glomerular diseases diagnosed between 2000 and 2012 in British Columbia, Canada. They identified 389 cases of lupus nephritis, 392 cases of membranous nephropathy, 818 of IgA nephropathy  — also known as Berger’s disease — 375 of focal segmental glomerulosclerosis, or FSGS, and 387 of ANCA-related glomerulonephritis (ANCA-GN). The patients were diagnosed with kidney biopsies.

Using census data, the researchers then assigned each individual to one of five socioeconomic levels, or quintiles, based on the average income and costs of living in their area of residence.

Next, the team calculated the incidence of each disease as a rate per 100,000 person-years in British Columbia. Person-years is a measure that takes into account both the number of people in a study and the amount of time each person spends in the study. The team then constructed statistical models to compare the relative risk of each disease in each income quintile.

The results showed that the incidence of disease increased with lower income in lupus nephritis and ANCA-GN. For instance, the incidence rate of lupus nephritis in women increased from 1.06 in the highest income quintile to 1.81 per 100,000 person-years in the lowest quintile.

These rates were lower in men, with 0.24 in the highest quintile and 0.40 in the lowest income group. Both sexes had a higher risk of lupus nephritis in the lowest quintile relative to the highest quintile (70% in women and 64 % in men). However, the lower number of men (66 compared to 323 women) means that this estimation is less precise, the team said.

Likewise, the incidence of ANCA-GN was 0.71 in the highest quintile and 1.06 in the lowest income group. This corresponds to a 50% greater risk of ANCA-GN in the lowest quintile.

For FSGS, there was a 55% higher risk in the lowest quintile, relative to those with higher income. In contrast, risk of membranous nephropathy and IgA nephropathy did not differ significantly across income groups.

These findings “emphasize the importance of identifying vulnerable populations of people who are at increased risk of developing these severe forms of kidney disease,” Mark Canney, PhD, of the University of British Columbia, the study’s lead author, said in a press release.

The exact reasons for this association between socioeconomic status and kidney disease are not totally clear.

“In particular, universal access to health care in Canada should minimize differences in missed or delayed diagnoses as supported by the broadly similar laboratory values at presentation across socioeconomic groups in the study,” Michelle M. O’Shaughnessy, MD, a nephrologist not involved in the study, wrote in an accompanying editorial.

“Accordingly, differences in disease incidence identified in this study are more likely to be explained by differences in health behaviors or social and environmental hazards than by inequitable access to preventative or diagnostic health care services,” she added

A better understanding of the relationship between socioeconomic status and kidney disease, “could inform future research regarding disease pathogenesis, as well as health policy directed toward vulnerable populations at increased risk of organ-threatening autoimmune diseases,” the scientists said.