A blood crossmatching apparatus, kit and methods for testing the compatibility of mammals for blood transfusion. Particulate layers in the apparatus allow nonagglutinated red blood cells to permeate through, while agglutinated red blood cells cannot. The apparatus also has a density solution layered above particulate layers. The density solution separates white blood cells from red blood cells in the whole blood when centrifuged, without lysing the red blood cells. Thus, the apparatus can be used to test whole blood.