Sickle cell anemia (SCA) patients experience organ damage that begins at an early age and results in significant morbidity and early mortality. Although all SCA patients share the same genetic mutation, the clinical complications are highly variable with some patients experiencing frequent and severe complications, while others have few serious complications. If SCA severity could be predicted early in life, those patients at greatest risk for complications could receive treatment prior to the onset of organ damage. No general SCA severity predictor or one that can be informative early in life exists. The investigators preliminary research has identified the absolute reticulocyte count (ARC) as a potential early predictive risk marker for SCA complications in pediatric patients. A higher ARC between ages 2 and 6 months of age is associated with an increased risk of hospitalization in the first 3 years of life; the mean ARC for the 36 patients who were hospitalized for SCA complications was significantly higher than that of the remaining 23 in those who were not hospitalized. Moreover, total hospitalizations were nearly three times higher by age 2 years in those infants who had an ARC of \> 200 than for those infants whose ARC was \<200. The proposed study will determine if ARC can be used as a risk-stratifier in asymptomatic infants with SCA and ascertain its value in targeting hydroxyurea therapy to those infants at highest risk of SCA sequelae.