Hemoglobin decline in children with chronic kidney disease: baseline results from the chronic kidney disease in children prospective cohort study.

BACKGROUND AND OBJECTIVES The level of glomerular filtration rate at which hemoglobin declines in chronic kidney disease is poorly described in the pediatric population. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS This cross-sectional study of North American children with chronic kidney disease examined the association of glomerular filtration rate, determined by the plasma disappearance of iohexol, and hemoglobin concentration. RESULTS Of the 340 patients studied, the mean age was 11 +/- 4 yr, the mean glomerular filtration rate was 42 +/- 14 ml/min per 1.73 m(2), and the mean hemoglobin was 12.5 +/- 1.5. Below a glomerular filtration rate of 43, the hemoglobin declined by 0.3 g/dl (95% confidence interval -0.2 to -0.5) for every 5-ml/min per 1.73 m(2) decrease in glomerular filtration rate. Above a glomerular filtration rate of 43 ml/min per 1.73 m(2), the hemoglobin showed a nonsignificant decline of 0.1 g/dl for every 5-ml/min per 1.73 m(2) decrease in glomerular filtration rate. CONCLUSIONS In pediatric patients with chronic kidney disease, hemoglobin declines as an iohexol-determined glomerular filtration rate decreases below 43 ml/min per 1.73 m(2). Because serum creatinine-based estimated glomerular filtration rates may overestimate measured glomerular filtration rate in this population, clinicians need to be mindful of the potential for hemoglobin decline and anemia even at early stages of chronic kidney disease, as determined by current Schwartz formula estimates. Future longitudinal analyses will further characterize the relationship between glomerular filtration rate and hemoglobin, including elucidation of reasons for the heterogeneity of this association among individuals.