Pathology Although more than 400 blood groups have been identified, the ABO blood group system remians the most impoant in clinical medicne because ? A It was the first blood group system to be discovered - B It has four different blood groups A,B, AB, 0 (H). C ABO(H) antigens are present in most body tissues and fluids D ABO(H) antibodies are invariably present in plasma when persons RBC lacks the corresponding antigen 💡 Explanation Although more than 400 blood groups have been identified, the ABO blood group system remians the most impoant in clinical medicne because ? ✓ Correct Answer: D. ABO(H) antibodies are invariably present in plasma when persons RBC lacks the corresponding antigen