This study looks at how long red blood cells (RBCs) last in people with sickle cell disease (SCD) who get regular blood transfusions. SCD is a condition where red blood cells become sickle-shaped and can cause problems like strokes. Regular transfusions help by giving normal-shaped RBCs. However, these transfusions sometimes don't work as well because the new RBCs don't last long. In this study, researchers will label some of the transfused RBCs with a special marker called biotin. Participants will return for check-ups frequently over six months to see how long these marked RBCs survive. The study is trying to find out what affects RBC survival so treatments can be improved.

• Participants need to visit often: weekly for the first 3 months, then monthly for 3 more months.
• No new treatments are given, just observing RBC survival after transfusions.
• Optional study with special RBCs, but you must meet specific requirements to join.