Patients who are experiencing a vaso-occlusive crisis will report to the clinic for treatment and screening into the SGSC-005 study. Patients who meet all inclusion/exclusion criteria will be randomized to receive either SANGUINATE 320 mg/kg or placebo (saline) over a 2 hour infusion period. Assessments of vital signs, ECGs, safety labs, adverse events as well as patient and physician questionnaires will be completed up to 6 hours after the start of the infusion. Patients will then be assessed for discharge either to home or admitted to the hospital for further treatment depending on their disease severity. Follow-up phone calls will be completed 24 hours and 7 days after initiation of treatment . A follow-up visit will be completed in the clinic at 72 hours after initiation of treatment.