Blood groups and transfusions

Definitions & Key takeaways

Blood groups are determined by the presence or absence of certain antigens on the surface of red blood cells. The most important blood group system is the ABO system, which is determined by the presence or absence of two antigens: A and B. People with blood group A have antibodies against the antigen B, people with blood group B have antibodies against the antigen A. People with blood group AB have no antibodies to either antigen, and people with blood group O have both types of antibodies. There is also the D antigen which determines rhesus (Rh). People who have this antigen are said to be Rh positive, while those who do not are Rh negative. Blood transfusion refers to the process in which a person receives whole blood, or components of blood. A person with type O negative blood can donate red cells to any other blood type regardless of the rhesus, while a person with type O positive blood can donate red cells to any other ABO rhesus positive recipient. Those which have AB positive can receive blood from any other ABO regardless of the rhesus, whereas those with AB negative can receive blood from any other ABO with rhesus negative.

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Introduction0:00–1:02

A blood transfusion is the procedure where a person receives blood, or elements of blood usually through an intravenous infusion - meaning through a vein.
Now - if you take blood and spin it in a centrifuge, the heaviest blood components move to the bottom, and the lightest ones move to the top.
Overall, three distinct layers form: the erythrocytes or red blood cells at the bottom, the buffy coat--which contains platelets and immune cells in the middle, and plasma at the top.
Now, in rare situations, like in traumatic injuries, someone might receive a whole blood transfusion, but more commonly a person is given one of the components of the blood.
For example, a person with anemia could just receive packed red blood cells, a person with clotting factor deficiency could get fresh frozen plasma which contains the coagulation factors, or someone with platelet deficiency might receive platelets.Now, most blood transfusions are homologous transfusions, where the blood comes from an anonymous donor.

Blood transfusions1:02–1:32

Sometimes the transfused blood is autologous, meaning the blood was taken out of the person at a prior time, like when they plan to have surgery in the near future.
In both cases, once the blood is taken, it’s mixed with sodium citrate which prevents the blood from coagulating, and then refrigerated or frozen for storage, or separated into its components by centrifuge.Now, before whole blood or packed red blood cells can be transfused, it’s important to know the blood typing of both the donor and the recipient of the blood.

Blood Type1:32–2:58

Every person has a unique blood group based on two classification systems: the ABO system and the Rh system. Both systems are based on the presence or absence of glycoproteins, which are proteins attached to a sugar molecule, found on the surface of red blood cells.
Now, if blood that has any of these glycoproteins is given to a person that has immune cells that have never seen those glycoproteins before, then the glycoproteins can act as antigens.
In other words, the recipient’s immune system might mistake the donor blood as an invader and mount an immune response. This is usually caused by recipient IgM antibodies that float around in the plasma.
These IgM antibodies can bind to multiple donor red blood cells, which can result in the red blood cells clumping together.
In addition, the IgM can activate complement proteins which form a membrane attack complex on the surface of the donor red blood cell causing pores to form and allowing the red blood cell to lyse.
This is called a hemolytic transfusion reaction. The IgM also activate other immune cells to cause a systemic immune response resulting in fever, hypotension, and rash.
Now, the ABO system refers to the type of glycoproteins found on a person’s red blood cells; you can have either type A, type B, type A and B glycoproteins, or neither, which is called type O blood.

ABO system2:58–4:11

The immune system produces antibodies against the glycoproteins that you don’t have. People with type A blood have antibodies to type B blood, and people with type B blood have antibodies to type A blood.
People with blood type AB don’t have antibodies to type A or type B blood, so they can receive blood from any of the blood types.
Thus, these lucky people are universal recipients. However since their red blood cells have both type A and type B antigens, they can’t donate blood to anyone except other AB blood type individuals.
So they’re good receivers but bad givers. On the other hand, people with type O blood have antibodies to both A and B glycoproteins, so people with type O cannot receive type A, type B, or type AB blood.
But since their red blood cells don’t have type A or type B antigens, they can donate blood to anyone. So they’re the universal donors, good at giving but bad at receiving.
Now, the other major blood group to be aware of is the Rh group, which gets its name from the animal in which the Rh protein was first described, the rhesus monkey.

Rh System4:11–5:19

Unlike the ABO system, people are either Rh positive, meaning they have the antigen on their red blood cells, or they are Rh negative, meaning it’s absent.
People that are Rh positive can receive both Rh negative or Rh positive blood since they do not have antibodies against the Rh glycoprotein.
But if an Rh negative person receives Rh positive blood, they could develop a hemolytic transfusion reaction. That's why we don't usually give Rh positive blood to Rh negative patients.
Having said that, we can do it in an emergency setting because these individuals don't have naturally occurring Rh antibodies, since Rh antibodies require prior exposure to Rh positive RBCs.
So, for someone who doesn’t have Rh antibodies, Rh positive blood might be okay the first time, but then they'll develop antibodies and you won't be able to give them Rh positive blood in the future.To prevent hemolytic transfusion reactions, blood must be typed and crossmatched.

Agglutination5:19–6:29

During blood typing, serum with known anti-A antibodies and anti-B antibodies are mixed with a person’s red blood cells.
If an agglutination reaction occurs, that means that the blood being tested has that glycoprotein on the surface. For example, if Anti-A serum is mixed with a person’s red blood cells and an agglutination reaction occurs, but does not when mixed with anti-B serum, then that person has blood type A.
The same procedure is also performed for people to determine a person’s Rh status. After the test, blood types are reported as the ABO group and then either negative or positive depending on the Rh status.
For example, a person with type A blood and without Rh factor would be called type A-. So if we combine the ABO and Rh classifications we get 8 possible blood types; A+, A-, B+, B-, AB+, AB-, O+, and O-.
Now, cross matching is a test to make sure a donor's blood is safe for a person to receive. During this process the recipient’s serum gets mixed with the donor's blood to see if an agglutination reaction occurs.

Cross matching6:29–7:00

If agglutination occurs, this means the recipient's blood contains antibodies against the donor's red blood cells, so that person cannot receive that donor’s blood.
This is helpful just in case there are additional glycoproteins that are causing a reaction beyond the ones identified in the blood typing.
Alright, as a quick recap... blood transfusion is a procedure where a person receives whole blood, or components of blood.

Review7:00–7:40

A person develops antibodies to the antigens not present in their own blood so if they receive blood containing that antigen, it will trigger a hemolytic transfusion reaction.
The antigens are glycoproteins on red blood cells that could be classified into the ABO or Rh system. In the ABO system people are either type A, B, AB, or O and in the Rh system they are either Rh positive or negative.
If blood is not properly crossmatched and typed, hemolytic transfusion reactions could occur. a hemolytic transfusion reaction,