Which blood group system was discovered first?

Which blood group system was discovered first?

• A. Rh
• B. ABO
• C. MNS
• D. Kell

Answer: (B)

ABO is the earliest discovered blood group system. Karl Landsteiner’s work in 1900 showed that red cells can carry A or B antigens (or both or neither) and that people have antibodies against the antigen they lack. This simple labeling—A, B, AB, or O—explained why some transfusions caused reactions and others did not, and it established blood typing as essential for safe transfusion practice. The Rh system and the other later-described systems like MNS and Kell were identified after ABO, in the mid-20th century, making ABO the first blood group system to be discovered.

ABO is the earliest discovered blood group system. Karl Landsteiner’s work in 1900 showed that red cells can carry A or B antigens (or both or neither) and that people have antibodies against the antigen they lack. This simple labeling—A, B, AB, or O—explained why some transfusions caused reactions and others did not, and it established blood typing as essential for safe transfusion practice. The Rh system and the other later-described systems like MNS and Kell were identified after ABO, in the mid-20th century, making ABO the first blood group system to be discovered.