Carbon Monoxide Levels and Sickle Cell Disease Severity

Background: \- Some people with sickle cell disease have different health problems than others. This may be related to how easily and frequently the red blood cells break apart in the blood. Researchers want to test breath and blood samples from people with sickle cell disease to look for very small amounts of carbon monoxide, which is produced when red blood cells break apart. They will compare these results with breath samples from healthy volunteers. Studying different levels of carbon monoxide may help predict what health problems a person with sickle cell disease may get. It may also provide more information on possible treatments. Objectives: \- To study breath carbon monoxide levels and their possible relation to the severity of sickle cell disease. Eligibility: * Individuals at least 18 years of age with sickle cell disease. * Healthy volunteers who are matched for age, sex, and race with the sickle cell disease group. Design: * Participants will be screened with a medical history. * Participants with sickle cell disease will provide a blood sample and have a heart function test. They will also breathe into a bag to provide an exhaled breath sample. * Healthy volunteers will provide an exhaled breath sample. * No treatment or care will be provided as part of this study.