Please select the eligibility criteria that correspond to the clinical trial below.
Title: N/A
Brief Summary: To determine how long blood transfusions are needed for primary stroke prevention. Also, to determine the duration of risk associated with abnormal transcranial Doppler ultrasound (TCD) and to determine the specificity of the stroke risk model developed in STOP 1 in patients with abnormal TCD measurements.


Options:
A: INCLUSION:

* Patient must have sickle cell anemia (hemoglobin SS) or sickle beta thalassemia (hemoglobin SB) as confirmed at the local institution.
* Participating institutions must submit documentation of the diagnostic hemoglobin analysis to the Statistical and Clinical Coordinating Centers to confirm the diagnosis of sickle cell anemia prior to randomization.
* Patient must be 5 through 14 years of age.
* Patient must have a cerebral infarct documented by MRI scan as read by the neuroradiology panel.
* Informed consent with assent in accordance with the institutional policies (institutional Institutional Review Board approval) and Federal guidelines (approved by the United States Department of Health and Human Services) must be signed by the patient's legally authorized guardian acknowledging written consent to join the study. When suitable, patients will be requested to give their assent to join the study.

EXCLUSION:

* Patient with a history of a focal neurologic event lasting more than 24 hours with medical documentation or a history of prior overt stroke.
* Patients with a transcranial doppler (TCD) study with a time-averaged mean velocity greater than 200 cm/sec verified by the study radiologist.
* Patients with other neurological problems, such as neurofibromatosis, lead poisoning, or tuberous sclerosis.
* Patients with HIV infection.
* Pregnancy.
* Patients who received treatment with anti-sickling drugs or hydroxyurea within 3 months or anticipate receiving anti-sickling drugs or hydroxyurea during the course of the study.
* Abnormal kidney function (creatinine \> 2x upper limit of normal).
* Patients on chronic blood transfusion therapy for other reasons.
* Patients judged not likely to be compliant by his/her hematologist and local nurse coordinator based on previous compliance in clinic appointments and following advice. Specifically, families that have missed at least two appointments without notification within 12 months prior to the trial or parents of potential patients that have been reported for medical or education neglect are not eligible for this trial.
* Patients unable to receive blood transfusion because of alloimmunization.
* Patients with permanent or semi-permanent metallic (braces on teeth) structures attached to their body. Such patients cannot obtain a MRI of the head to assess the presence of silent cerebral infarcts.
* Siblings randomized in the trial.
B: Pediatric patients, ages 24 months to 16 years, with sickle cell anemia or S-beta zero thalassemia.
C: No eligibility criteria
D: Inclusion Criteria:

1. Pediatric subjects with severe forms of sickle cell anemia (HbSS, HbSβ0 thalassemia, HbSD, HbSOArab)
2. Age: ≥ 2 and \< 11 years of age, at the time of enrollment
3. Conditional TCD Velocity (170 - 199cm/sec) by Transcranial Doppler ultrasonography examination within 3 months of enrollment
4. Parent or guardian willing and able to provide informed consent
5. Ability to comply with study related treatments, evaluations, and follow-up

Exclusion Criteria:

1. Prior abnormal TCD Velocity
2. History of clinical stroke
3. Inability to take or tolerate daily oral hydroxyurea, including

   * Known allergy to hydroxyurea therapy
   * Known positive serology to HIV infection
   * Known malignancy
   * Current lactation
4. Abnormal laboratory values at initial evaluation (temporary exclusions):

   * Hemoglobin concentration \< 6.0 gm/dL
   * Absolute reticulocyte count \< 100 x 10\^9/L with a hemoglobin concentration \< 8.0 gm/dL
   * WBC count \< 3.0 x 10\^9/L
   * Absolute neutrophil count (ANC) \< 1.0 x 10\^9/L
   * Platelet count \< 100 x 10\^9/L
5. Current use of therapeutic agents for sickle cell disease (e.g., hydroxyurea, arginine, decitabine, magnesium, chronic transfusions). Subjects must be off therapeutic agents for sickle cell disease for at least 3 months prior to enrollment.
6. Current participation in other therapeutic clinical trials
7. Serum creatinine more than twice the upper limit for age OR ≥ 1.0 mg/dL
8. Any condition or chronic illness, which in the opinion of the clinical investigator makes participation ill-advised
9. Pregnancy (for post-menarchal females only)
10. Erythrocyte transfusion within the past 2 months
11. Previous stem cell transplant or other myelosuppressive therapy

Answer: C