History of immunohematology — Who discovered and first described the ABO human blood group system?

Introduction / Context:
The ABO blood group system is fundamental to transfusion medicine. Its discovery made safe blood transfusions possible by preventing hemolytic reactions caused by incompatible donor–recipient pairings.

Given Data / Assumptions:

• We need the scientist credited with discovering ABO blood groups.
• Several historical figures are listed; only one is correct.
• The discovery predates modern molecular immunology.

Concept / Approach:
Karl Landsteiner, an Austrian physician, identified the ABO system in 1900–1901 by observing agglutination reactions among human sera and red cells. He later received the Nobel Prize in Physiology or Medicine (1930) for this work. His findings underpin crossmatching and compatibility testing used worldwide.

Step-by-Step Solution:

Verification / Alternative check:
Standard transfusion medicine texts and Nobel archives confirm Landsteiner’s role and timeline.

Why Other Options Are Wrong:

• Theodor Kocher: pioneering surgeon (thyroid surgery), Nobel 1909.
• Otto Warburg: cellular respiration and Warburg effect, Nobel 1931.
• Karl Hooper: not associated with ABO discovery.

Common Pitfalls:
Confusing later refinements (e.g., Rh system) with the original ABO discovery.

Final Answer:
Karl Landsteiner