दो सबसे महत्वपूर्ण रक्त समूह प्रणालियों की खोज रक्ताधान के साथ शुरुआती प्रयोगों के दौरान की गई हैं : ABO समूह ( ) सं १९०१ में और Rhesus समूह ( ) १९३७ में.Development of the Coombs t est ( ) in 1945 , the advent of transfusion medicine ( ) , and the understanding of hemolytic disease of the n ewborn ( ) led to discovery of more blood groups , and now 29 human blood group s ystems ( ) are recognize d by the International Society of Blood Transfusion ( ) ( ISBT ) , and acros s the 29 blood groups , over 600 differen t blood group antigen s have been found , but many of these are very rare or are mainly found in certain ethnic groups .
Entity: रक्त — Type: /food, /body_part