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Association of income level with kidney disease severity and progression among children and adolescents with CKD: a report from the Chronic Kidney Disease in Children (CKiD) Study.

BACKGROUND
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; but its impact on young people with CKD is not established.


STUDY DESIGN
Prospective cohort study.


SETTINGS & PARTICIPANTS
572 children and adolescents aged 1-16 years with mild to moderate CKD residing in the United States and Canada who were enrolled in the Chronic Kidney Disease in Children (CKiD) Study.


PREDICTOR
Self-reported annual household income category as a proxy measure for SES: ≥$75,000 (high income), $30,000 to <$75,000 (middle income) and <$30,000 (low income).


OUTCOMES & MEASUREMENTS
Clinical characteristics and CKD severity at baseline (glomerular filtration rate [GFR] and comorbid conditions related to disease severity and management) and longitudinally (GFR decline and changes in blood pressure z scores and height z scores per year).


RESULTS
At baseline, low and middle household incomes, compared to high income, were associated with minority race (39% and 20% vs. 7%), lower maternal education (28% and 5% vs. 1%), abnormal birth history (34% and 32% vs. 21%), and having at least one clinical comorbid condition (66% and 64% vs. 55%). Baseline median GFRs were similar across income categories (43-45 mL/min/1.73 m2). After adjusting for baseline differences, average GFR declines per year for the low-, middle-, and high-income categories were -2.3%, -2.7%, and -1.9%, respectively, and were not statistically significantly different among groups. Blood pressure control tended to improve in all groups (z score, -0.10 to -0.04) but higher income was associated with a faster improvement. Each group showed similar deficits in height at baseline. Height deficits diminished over time for participants from high-income families, but not among those from low-income families (z scores for height per year, 0.05 and -0.004, respectively; P = 0.03 for comparison of high and low income).


LIMITATIONS
Income is an imperfect measure for SES; CKiD participants are not representative of children and adolescents with CKD who are uninsured or not receiving care; statistical power to detect associations by income level is limited.


CONCLUSIONS
GFR decline was similar across income groups but better improvement in BP was observed among those with high income. Children and adolescents with CKD from lower income households are at higher risk of impaired growth.