How is blood type compatibility determined?
Blood types are grouped into 8 categories by combining the ABO system (A, B, O, AB) with the Rh system (+, -). A transfusion is safe only when the antigens on red blood cells and the antibodies in plasma don't react against each other, so not every blood type can be freely given to every other type.
Universal donors and universal recipients
People with O- blood have no A or B antigens at all, so their blood can be given to any blood type β earning it the name "universal donor." On the other end, people with AB+ blood already carry every antigen, so they can receive blood from any type, earning it the name "universal recipient."
A note on accuracy
This page summarizes the general principles of transfusion compatibility. Actual transfusions must always go through a medical team's precise crossmatch test. Outside of emergencies, the standard practice is to transfuse using the same blood type.
Frequently Asked Questions
What about blood type and personality?
The idea that blood type determines personality is a popular-culture belief with no scientific backing. If you'd like to explore it just for fun, check out our Blood Type Personality page.
Why does blood type distribution differ by country?
Blood type distribution varies by country due to differences in genetic ancestry across populations. For example, type B is relatively common across East Asia, while type O is relatively common among Indigenous peoples of South America.