1. Presence of a pain crisis that prevents patient from engaging in normal activities.
2. Presence of acute infection, injury, surgery, asthmatic episode or other acute complication
3. Hemoglobin A only phenotype, hemoglobin S trait or hemoglobin C trait.
4. Less than three weeks has elapsed since hospitalization, ER visit, or Doctor's Office visit for pain crisis, acute chest syndrome, infection or other complication of SCD.