Sickle cell disease (SCD) is a blood disorder where red blood cells (RBCs) die too early, causing a shortage of healthy cells. This study wants to find out how long RBCs last in people with SCD and other blood disorders, especially before and after treatment or a bone marrow transplant. Participants must be 18 or older, with SCD or a similar disorder, and those who had a transplant. In this study, about 7 tablespoons of blood will be taken and mixed with biotin (a type of vitamin) that sticks to RBCs. The next day, these biotin-labeled RBCs are returned to the participant. Participants come back for regular visits to have smaller blood samples taken to see how many biotin-labeled RBCs are still there. This may happen every 2-4 weeks for up to 20 weeks.

• Duration: Up to 20 weeks, with regular visits.
• Eligibility: Adults 18+ with SCD or related disorders, post-transplant patients.
• Risks: Exclusion if allergic to biotin or recent blood transfusions.