Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
The ABO blood group system classifies human blood based on the presence or absence of antigens A and B on red blood cells. This system is crucial in transfusion medicine and can trigger immune responses if incompatible blood types are mixed.
5 Must Know Facts For Your Next Test
The four main ABO blood groups are A, B, AB, and O.
Type O blood lacks both A and B antigens but has anti-A and anti-B antibodies, making it a universal donor.
Type AB blood has both A and B antigens but lacks antibodies against them, making it a universal recipient.
Incompatible blood transfusions can cause severe immune reactions due to antibody-mediated destruction of red blood cells.
The ABO system is genetically determined by the inheritance of alleles from parents.