ANTONIA REEVE / SCIENCE PHOTO LIBRARY ANTONIA REEVE / SCIENCE PHOTO LIBRARY
Blood group test results. Hand holding a set of centrifuge tubes with four negative (left) and two positive (right) results for a blood group test. The blood was mixed with an antibody to test for an antigen in the blood. If the antibody did react with the antigens on the red blood cells, the red blood cells stick together (agglutinate). The gel (pale blue) then filters out agglutinated cells as the samples are spun rapidly in a centrifuge. The normal red blood cells sink to the bottom of the tubes. Blood is grouped by its antigens so as to prevent potentially fatal immune reactions in the patient who receives the blood. For a sample of blood before centrifuging, see image M530/465.
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