43 human systems are identified as of June 2021. When it comes to blood transfusions, the ABO blood group system is the most important one. When it comes to pregnancies, the Rh blood group system is the most important one. The name rhesus factor (Rh) goes back to the use of erythrocytes extracted from the blood of rhesus monkeys for obtaining the first blood serum. The Rh blood group system consists of 49 defined blood group antigens among which the five antigens D, C, c, E, and e are the most important. There is no d antigen. Rh(D) status of an individual is normally described with a positive (+) or negative (−) suffix after the ABO type (e.g., someone who is A+ has the A antigen and Rh(D) … Continue reading The Rh Negative Blood Factor