Human Blood Groups

Definition

A classification of human blood based on the presence or absence of specific antigens on the surface of red blood cells, chiefly the ABO and Rh systems.

Key points

• The ABO system has four groups: A, B, AB, and O, decided by A and B antigens on red cells and the matching antibodies in plasma.
• Group O (Rh negative) is the universal donor because its red cells carry no A or B antigen; group AB (Rh positive) is the universal recipient because its plasma has no anti-A or anti-B antibody.
• The Rh factor is a separate antigen; a person is Rh positive if it is present and Rh negative if absent, so a full type is written as A positive, O negative, and so on.
• Karl Landsteiner discovered the ABO blood groups (1901) and won the Nobel Prize; mismatched transfusion causes clumping (agglutination) of red cells and can be fatal.
• An Rh negative mother carrying an Rh positive baby can develop antibodies that harm a later Rh positive baby (haemolytic disease of the newborn), prevented by an anti-Rh injection.

Why it matters for CAPF

The four ABO groups, universal donor and recipient, the Rh factor, Landsteiner's discovery, and the risk of mismatched transfusion are standard biology facts, relevant also to emergency and field medical readiness.

Common confusion

O negative is the universal donor and AB positive is the universal recipient; the two are opposites and are easy to reverse. The ABO group and the Rh factor are independent, so a person is described by both together.

Related concepts

concept types of immunity, concept genetic disorders, concept vitamins and deficiencies

Parent note

human body and systems