Asthma in the sickle cell patient is likely to have a molecular fingerprint which can be distinguished from asthma in the non-sickle cell patient. The investigator's specific aim is to compare the urinary metabolomic profile of children with asthma and sickle cell disease to children without asthma who have sickle cell disease, and to a cohort of African American children with asthma but without sickle cell disease. The hypothesis is that children with asthma and sickle cell disease will have a unique metabolomic profile that will discriminate these patients from children with sickle cell disease who have respiratory dysfunction that is not asthma, and from children with asthma who do not have sickle cell disease.