Which of the following is a transfusion science test?

The direct antiglobulin test (DAT) is a key test in transfusion science, as it is used to detect antibodies that are bound to the surface of red blood cells. This is particularly important in blood transfusions because it helps to identify potential incompatibilities between donor and recipient blood. The test provides critical information when assessing for hemolytic anemia or ensuring safe transfusion practices.

The other options are tests that serve different purposes. Alpha-fetoprotein (AFP) is primarily used as a tumor marker in oncology for liver cancer and germ cell tumors. Ammonium (NH4) testing is related to liver function assessment and metabolic disorders, rather than transfusion needs. C-reactive protein (CRP) is an inflammatory marker used to assess inflammation or infection in the body. Therefore, the DAT is directly related to transfusion science, making it the correct choice in this context.