Even with more prescriptions for growth hormone, children and adolescents with chronic kidney disease were less likely to grow to normal height ranges if they came from lower-income families, according to research funded by the National Institutes of Health. Results from the Chronic Kidney Disease in Children (CKiD) Study were published in the December issue of the American Journal of Kidney Diseases.

The children with lower socio-economic status (SES) who had CKD were likely to be substantially shorter than children their age from all income levels who didn’t have the disease. Also, among all children with CKD, those from lower-income families were likely to be shorter than those from higher-income families. All participants had health insurance, a pediatric nephrologist, and no other known cause of growth deficiency.

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Unlike findings from studies in adults, kidney disease progressed at similar rates across all income groups in CKiD. This came as a surprise to investigators, who said they expected faster kidney function decline with lower SES, as is found in adult CKD. Disease progression was defined by a decline in estimated glomerular filtration rate.

CKiD, the largest study of children with CKD, is the first to study the effects of income on kidney disease progression and complications in this population. The current study examined growth failure, common in children with CKD, because the disease can interfere with the normal effect of a child’s own growth hormone.

“Since these lower SES children received higher proportions of prescriptions for growth hormone, it’s possible that these families are not filling all their prescriptions or are filling them but not sticking to their treatment regimen as closely as higher-income families are,” said Dr. Marva Moxey-Mims, a pediatric kidney specialist at the NIH’s National Institute of Diabetes and Digestive and Kidney Diseases, the study’s primary funder. “Although there also could be other issues like nutrition or household finances contributing to this difference, the main lesson is that we may need to learn how to help families better follow treatment plans for their children with CKD.”

Moxey-Mims said that more research is proposed in CKiD to examine treatment adherence, and a partnership with the NIH-supported Chronic Renal Insufficiency Cohort Study (in adults) will look at associations between health literacy and SES.

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SES was based on reported annual family income: $75,000 or higher (high), $30,000 to $75,000 (middle), and less than $30,000 (low). Low and middle household incomes were more often associated with minority ethnicity (African-American and Latino), compared to higher income – 39% and 20% vs. 7%.

About the Chronic Kidney Disease in Children Study
CKiD is a multicenter prospective study of children ages 1 to 16 years with mild to moderate impairment of kidney function. Forty-eight sites in the United States and two in Canada are following more than 600 children. Children's Mercy Hospital at the University of Missouri-Kansas City School of Medicine and The Children's Hospital of Philadelphia at the University of Pennsylvania are the study’s clinical-coordinating centers. The Johns Hopkins Bloomberg School of Public Health in Baltimore is the data-coordinating center. The ongoing CKiD study aims to determine risk factors for declining kidney function and to understand how the decline affects cognitive function, behavior, growth failure and the risk for cardiovascular disease.