A medication recently approved in the U.S. for multiple myeloma treatment that is really just an antibody! Daratumumab (“DARA” for short) is simply a monoclonal antibody against a cell protein called “CD38.” CD38 is particularly abundant on the surface of plasma cells (the malignant cell in myeloma), and the DARA anti-38 has been clearly shown to damage and destroy malignant plasma cells in patients with myeloma who have failed other treatments. This is a very good and exciting thing, since multiple myeloma is a really, really difficult disease to treat! Unfortunately, CD38 is not only present on plasma cells, but is also found in much smaller quantities on red blood cells. As a result, everyone who gets DARA also gets a built-in blood bank testing challenge. Because all reagent RBCs will carry CD38, patients who are taking DARA will have positive antibody screens, antibody identification panels with panagglutins that look like warm autoantibodies, and incompatible AHG crossmatches (NOTE: ABO and Rh testing is not affected; only those tests that have an anti-human globulin phase). We can combat this, IF we know that the patient is on DARA. I discussed this extensively in a Blood Bank Guy Essentials Podcast episode from May 2016.