A membrane protein involved in mobilizing intracellular calcium, expressed on many cells (most prominently plasma cells, but also weakly on RBCs). In blood banking, CD38 is important because of the multiple myeloma drug daratumumab (DARA), approved in the U.S. in November 2015. DARA is a monoclonal antibody against CD38, currently approved for use in myeloma patients who have relapsed. These patients may take large doses of DARA for a long period of time. Since DARA binds to CD38 anywhere CD38 is present, the drug also binds to all RBCS (including, when serum is added, the reagent RBCs that are used for testing patients for unexpected antibodies). As a result, patients on DARA appear to have a weak panagglutinin that is easily confused with a warm autoantibody. We can avoid the issue by treating our testing cells with DTT, which removes CD38 (as well as Kell system and a other less important RBC antigens) and eliminates the panagglutinin effect. The effect, by the way, appears to be a laboratory issue, as RBCs transfused to those with anti-CD38 seem to survive normally (or close to normally).