Hemoglobin differences by race in children with CKD

Abstract

Background: There are known racial disparities in the prevalence of anemia in adults with chronic kidney disease (CKD), but these differences have not been well described in children.

Study design: Cohort study, cross-sectional analysis.

Setting & participants: The Chronic Kidney Disease in Children (CKiD) Study is a multicenter prospective cohort study of children with mild to moderate CKD. This analysis included 429 children of African American or white race.

Predictor: Race.

Outcomes & measurements: This study examined the association of race with hemoglobin level. Both multiple linear regression and generalized gamma modeling techniques were used to characterize the association between race and hemoglobin level.

Results: 79% of the cohort was white, 21% was African American. Neither median hemoglobin level nor frequency of erythropoiesis-stimulating agent use differed by race. In multivariate analysis, lower levels of iohexol-measured glomerular filtration rate, African American race, and glomerular disease (vs nonglomerular disease) as the underlying cause of CKD were independently associated with decreased hemoglobin levels; independent of glomerular filtration rate and CKD diagnosis, African American children had average hemoglobin levels that were 0.6 g/dL (95% CI, -0.9 to -0.2 g/dL) lower than those of white children. Generalized gamma modeling showed that differences in hemoglobin levels observed by race become more pronounced when moving from high to low in the overall hemoglobin level distribution.

Limitations: Cross-sectional analysis cannot establish causality, and data for iron stores were not available for all patients.

Conclusions: African American compared with white children have lower hemoglobin values in CKD independent of the underlying cause of CKD. These racial differences in hemoglobin levels appear to increase at the lower end of the hemoglobin level distribution in this population.

Figure 1

Scatterplot of hemoglobin (Hb) vs. log-transformed iohexol-measured glomerular filtration rate (mGFR) by race. White children (N=338) are depicted with open circles; African-American (A-A) children (N=91) are depicted with solid circles. Race -specific linear regression lines of Hb on log(mGFR) are overlayed. Regression line for white children is a dashed line,; for A-A children is a solid line.

Figure 2

Percentile plots displaying the distribution of hemoglobin (Hb) levels for children not using (n=364) versus using (n=91) erythropoietin stimulating agent (ESA) by race. Plots for African-American (A-A) children are shown with solid lines; plots for White children are shown with dashed lines.

Figure 3

Univariate, race-specific generalized gamma derived probability density curves of hemoglobin (Hb) with left-censoring for current erythropoietin stimulating agent (ESA) users. The Hb distribution for African-American children [GG(2.55, 0.14, 0.86)] is shown with a solid line; Hb distribution for white children [GG(2.54, 0.12, 0.41)] is shown with a dashed line. The shaded areas show that 28% of African American children (striped area) compared to only 16% of white children (solid grey area) are estimated to have a Hb <11 g/dL.

Figure 4

Relative percentile plot of hemoglobin (Hb) for 81 African-American (A-A) vs. 404 white children, based on multivariate generalized gamma modeling with left-censoring for current erythropoietin stimulating agent (ESA) users. Covariates in the generalized gamma model include: sex, body mass index z-score, pubertal status, iohexol-measured glomerular filtration rate, glomerular cause of CKD, and current use of iron supplements.