Stabilization Phase: Patients take 2 hydroxyurea tablets a day until their fetal hemoglobin levels stabilize, usually over 2 to 4 months. They have blood tests every 2 weeks to monitor hemoglobin and fetal hemoglobin levels. At some time during this period, they undergo a test to measure kidney function, in which they are injected with an iodine-containing dye and wear a small pump for 1 day that injects a small amount of dye under the skin over 24 hours. They come to the clinic for 2 or 3 blood tests collected over 4 hours.