Fetal Hemoglobin in Sickle Cell Anemia: Determinants of Response to Hydroxyurea

Hydroxyurea (HU) can increase fetal hemoglobin (HbF) in kg. All four quartiles had substantial increases of F cells in sickle cell anemia (HbSS). To identify determinants of the the first year. This was maintained for 2 years only in the top HbF response, we studied 150 HU-treated patients grouped three quartiles. Leukocyte and reticulocyte counts decreased by quartiles of change in HbF from baseline to 2 years. Half initially in all quartiles, but drifted back toward baseline levof the HU-assigned patients had long-term increments in els in the lowest HbF response quartile. Initial HbF level and HbF. In the top two quartiles, HbF increased to 18.1% and phenotype of the F-cell production (FCP) locus were not as8.8%. These patients had the highest baseline neutrophil sociated with HbF response, but absence of a Central African and reticulocyte counts, and largest treatment-associated Republic (CAR) haplotype was. Bone marrow ability to withdecrements in these counts. In the lower two quartiles, 2stand HU treatment may be important for sustained HbF year HbF levels (4.2% and 3.9%) and blood counts changed increases during HU treatment of HbSS. little from baseline. In the highest HbF response quartile, This is a US government work. There are no restrictions on myelosuppression developed in less than 6 months, compliits use. ance was best, and final doses of HU were 15 to 22.5 mg/