What discovery in the 20th century made it possible to administer blood transfusions safely?

The discovery of the main blood groups was a pivotal moment in the field of medicine, particularly relevant to the safe administration of blood transfusions. Before the identification of blood groups, there were significant risks associated with transfusions due to the potential for incompatible blood types to be mixed, which could lead to severe reactions and even death. The ABO blood group system, discovered by Karl Landsteiner in 1901, allowed for the categorization of blood into distinct groups (A, B, AB, and O). This categorization made it possible to match donors and recipients more accurately, significantly reducing the risk of transfusion reactions.

By understanding the specific antigens present on red blood cells, healthcare providers could ensure compatibility, which is essential for safe transfusion practices. This understanding was foundational for the development of blood donation and transfusion protocols, leading to advances in both surgical and medical treatments.

While sterile techniques, anticoagulants, and blood typing machines are indeed important components of modern transfusion practices, they build upon the foundational knowledge established by the discovery of blood groups. Without this critical advancement, the risk associated with blood transfusions would remain unacceptably high, highlighting why it is the correct answer in this context.