Among adults, lower socioeconomic status (SES) is a risk factor for chronic kidney disease (CKD), progression to end-stage renal disease, and poor health outcomes. However, the effect among children with CKD is not well known. The Chronic Kidney Disease in Children (CKiD) study looked at this question in a recent publication in AJKD. Three authors of this study, Dr. Susan Furth (SF), Dr. Guillermo Hidalgo (GH), and Dr. Derek Ng (DN) discuss this topic with Dr. Sidharth Sethi (eAJKD), eAJKD Advisory Board member.
eAJKD: What prompted you to do this study?
DN: In the US, adults with lower SES have higher rates of CKD and end-stage renal disease, as well as more comorbidities associated with kidney function decline compared to those from higher economic strata. However, how SES affects children with CKD is largely unknown. Children are dependent on caregivers for their health needs, like managing medications and visiting doctors, as well as providing a safe environment and nutrition. It is clear that family income can affect parents’ abilities to comfortably meet these needs, so we wanted to understand how family household income might impact the disease severity and progression of a CKD in a child.
eAJKD: Do you think that if this study was done in a developing country, with more uninsured children, your results would have been different?
SF & GH: We have no data to directly answer this question. It is only guesswork to generalize our results from a North American CKD population to that of a developing country which may not have subspecialty care, or whose socioeconomic distribution is vastly different from the US and Canada. However, from the personal perspective of one of our co-authors, Dr Hidalgo, who has worked as a nephrologist in developing countries, greater differentials in access to care and exposure to environmental toxins among the economically disadvantaged would likely exaggerate the differences in comorbidities and risk for GFR decline that we saw in this study.
eAJKD: For the cross sectional analysis at study entry, you hypothesized that lower SES is associated with higher disease severity, defined by the number of comorbid conditions (hypertension, anemia, abnormalities of bone-mineral metabolism, and growth). For the longitudinal analysis, you hypothesized that children with CKD from lower SES families have more rapid GFR decline, worse blood pressure (BP) control, and poor linear growth. What led you to these hypotheses?
DN, GH, & SF: The adult literature has consistently reported poor health outcomes among people with low SES (including low income), and those findings informed our hypotheses that low income would be associated with increased disease severity and accelerated progression. We found that most children had elevated BP upon study entry, but those from high income households were able to reduce their BP faster than those from low income households, even after adjustment for important confounders. Similarly, most of these children with CKD had substantial deficits in height. On average, the height deficits in children from high income households diminished over time, but this was not true for children from low income households.
eAJKD: Longitudinally, there was a similar decline in kidney function across all income categories. Do you think a larger sample size would have made a difference?
DN: It is not clear whether a larger sample size would have produced different results. The CKiD study initially enrolled children with moderate to severe CKD (the cohort had a median GFR level of 44 mL/min/1.73 m2). The similar decline in kidney function across all income levels is likely related to the comparable GFR levels at which these children entered the study, and attests to the devastating disease process of CKD. Importantly, despite the similar GFR decline, poor management of blood pressure and persistent deficits in height were also more common among children from low income families compared to children from high income families.
eAJKD: Based on your study, can you comment on adherence to medical care in different income groups?
DN & SF: Unfortunately, direct assessment of adherence to medical treatment in the study is limited. We suspect adherence may play a role since this has been observed in studies of adults. Low income households may have fewer resources to pay for medications, access a pharmacy or clinic, or pay for insurance. Nearly all of the participants had some form of health insurance, which is encouraging since having insurance is one less barrier to receiving care. Families with low household income were more likely to have public rather than private insurance, but nevertheless they were insured. This is important to note, since our results may not generalize to children with CKD who do not have insurance or are not receiving regular specialty care. We suspect these children will have worse outcomes compared to the CKiD cohort. With health insurance coverage expected to expand in the future, it is encouraging to note that in this cohort where nearly everyone had some form of health insurance, having low income was not associated with faster GFR decline.
eAJKD: Based on the results of your study, are there any plans for further prospective studies?
SF: The Chronic Kidney Disease in Children cohort is a multicenter, prospective study that is continuing to collect data. We have been extremely fortunate to have had the continuous support of the NIDDK, NHLBI, and NICHD, and recently the study was renewed for another 5 years. A second round of recruitment of children with earlier stage CKD is nearing completion. We are very grateful for the time and effort of the children, adolescents, and families who have participated, and continue to participate in CKiD.
We plan to continue to identify risk factors that make some children particularly vulnerable to more rapid CKD progression and the development of comorbidities. We hope our findings spur interventional studies to slow CKD progression and prevent the development of cardiovascular disease as we have found that these occur at an alarming rate in this young population.