The transfusion medicine (blood and blood product transfusion) is basically the study of antigen and antibodies to RBCs (red blood cells). The two most important factors of blood transfusion are ABO antigens and antibodies and Rh system, most important being the ABO blood group antigen system and Rh system is the second most important factor in transfusion medicine. Other factors such as transmission of infectious agents, immunologic and non immunologic reaction of blood and blood product transfusion are secondary to ABO blood group antigen system and Rh system.

What is the importance of ABO antigens and antibodies?

The ABO antigen system is the most important in blood and blood product transfusion (also called transfusion medicine) and was first recognized in the year 1900. The ABO antigens are present in the plasma and other body fluids as glycoprotein, although the ABO antigens are carbohydrates and attached to lipids glycosphingolipids or proteins (glycoprotein). H substance is the precursor on which antigen A and antigen B are attached. Addition of N-acetylgalactosamine forms antigen A and addition of galactose produces antigen B. individuals who can not form H substance due to lack of the gene form Bombay phenotype (Bombay blood group).

During the time of evolution of humans, the food supply was intermittent and for survival there was need to store energy in excess of what is required for immediate use. Fat cells did the job of storing energy, which are widely distributed in adipose tissues. The fat cells can store excess energy efficiently as triglyceride and, when needed, release stored energy as free fatty acids for use at other sites. This physiologic system developed during the time of evolution acts through endocrine and neural pathways and even can permit humans to survive starvation for as long as several months. But at present era of nutritional abundance, sedentary lifestyle, and influenced importantly by genetic endowment, this physiologic system of storing energy in adipose tissues can produce obesity and adverse health consequences due to obesity.