In sickle cell disease (SCD), hydroxyurea (HU) treatment decreases the number of vaso-occlusive crisis (VOC) and acute chest syndrome (ACS) by increasing fetal hemoglobin (HbF). Data are lacking regarding the frequency of HU dose modification or whether sub-therapeutic doses (<15 mg/kg/day) are beneficial. We reviewed the medical records of 140 patients from 2010 to 2014. The laboratory parameters and SCD complications were compared between the first and last visits based on HU use. Fifty patients (36%) never took HU or suspended HU ("no HU" group). Among patients taking <15 mg/kg/day HU on their first visit, half remained at the same dose, and the other half increased to ≥15 mg/kg/day. Among patients taking ≥15 mg/kg/day, 17% decreased to <15 mg/kg/day, and 83% stayed at ≥15 mg/kg/day. The "no HU" group had fewer episodes of VOC and ACS. Both HU treatment groups had a reduction in both complications (p < 0.0001). This improvement was observed in all SCD phenotypes. The white blood cell (WBC) counts were found to be lower, and HbF increased in both HU groups (p = 0.004, 0.001). The maximal HbF response to HU in HbS/β⁺-thalassemia was 20%, similar to those observed for HbSS (19%) and HbS/β⁰-thalassemia (22%). HbS/β⁺-thalassemia could have a similar disease severity as HbSS or HbS/β⁰-thalassemia. Patients with HbS/β⁰-thalassemia or HbS/β⁺-thalassemia phenotypes responded to HU.
Keywords: fetal hemoglobin; hydroxyurea; sickle beta thalassemia; sickle cell disease.