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.

Blood and blood products are collected as whole blood from donors in various anticoagulants. The blood and blood products which are used for transfusion are whole blood, packed red blood cells (PRBCs), platelet concentrates, fresh frozen plasma (FFP), cryoprecipitate, and plasma derivatives. Plasma derivatives are also used for transfusion such as albumin, intravenous immunoglobulin, anti-thrombin, and coagulation factor concentrates. Plasma derivatives are generally collected from several donors and pooled together and infectious organisms are removed by treating.

Separation of blood components from whole blood:

Blood is collected as whole blood of 450 ml (one unit of blood) in various anticoagulants. The whole blood is then processed to produce blood various blood components mentioned above. Most commonly blood is transfused as whole blood. To get blood components, whole blood is first separated by slow centrifugation into PRBCs and platelet rich/concentrated plasma.

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).

Generally adverse reactions of blood transfusion are (1) non immune mediated and (2) immune mediated. Fortunately the common adverse reactions that occurs after blood transfusion are mild and serious adverse reactions occur only rarely, if ever.

The blood transfusion may also be complicated by transmission of infectious agents, such as virus, bacteria, and other infectious agents. Fortunately the transmission of infectious agents is also rare, especially viral transmissions are becoming rarer due to pretransfusion screening of donor’s blood.

What are the non immune mediated adverse reactions that can occur?

The non immune mediated adverse reactions that can occur after transfusion of blood and blood components are volume overload, hypothermia (subnormal body temperature), electrolyte imbalance (mainly toxicity), iron overload, hypotensive reactions and immunomodulation etc.

You can find here What Infections can be Transmitted by Blood Transfusion?

Several adverse reactions to blood transfusion can occur despite checking, inspecting and testing at several levels. Fortunately, the common adverse reactions to blood transfusion are minor and serious reactions occur very rarely if ever. If any adverse reaction is suspected, the blood transfusion should be stopped immediately and reported to blood bank for investigation.

Commonly two types of adverse reactions to blood transfusion are seen, (1) immune mediated adverse reactions and (2) non immunologic adverse reactions. Complications due to infectious organisms may also occur in blood transfusion.

What are the immune mediated adverse reactions to blood transfusion?

The immune mediated adverse reactions to blood transfusion are FNHTR or febrile non hemolytic transfusion reaction (occurs 1-4 out of 100 units of blood transfusions or 1-4:100),

Blood and blood products transfusion can be life saving, but if not done appropriately and with appropriate precaution, blood transfusion can also cause problem to the recipient of the transfused blood. The complications that can occur due to blood transfusion includes, transmission of infectious agent (from donor to recipient), immunologically mediated adverse reactions (such as hemolysis, graft-versus-host reaction, anaphylactic reaction etc.), non-immunologically mediated adverse reactions such as hypothermia, fluid overload, electrolyte excess etc.

There are several infectious agents that can be transmitted through blood transfusion, but practically very rarely seen in clinical practice due to rigorous screening of blood for infectious agents before transfusion,