Blood Typing

Antigens on Erythrocytes

Before diving into blood typing, we first have to understand about antigensMolecules on the surface of cells that trigger an immune response. and antibodies, officially called immunoglobulins(Ig) Antibodies: Proteins produced by the immune system to target specific antigens..  Antigens are on erythrocytes(RBCs): Red blood cells responsible for oxygen transport. and antibodies are floating around in plasmaThe liquid component of blood.. The antigens that you have on your red blood cellsThe basic structural and functional units of life. is a product of genetics.  All human have genes for the antigens in the plasma membranes of their red blood cells.  You can have genes that insert what we call the A antigen or the B antigen. Alternatively, the gene can contain instructions to make no antigen. 

If all you have is the A antigen in your red blood cells, then you have the A type blood. This is according to the ABO blood typing system.  If all you have is B, you have blood type B.  If you have both, good for you!  You have AB type blood.  And, finally, if you have none, you are a freak of nature.  I’m kidding.  If you have none then, like me, you have blood type O.  These are the types of blood resulting from the ABO blood types.  We will consider the positive or negative separately.

Immunoglobulins in Plasma

Whatever antigen you have, you don’t have that antibody.  If you are type A, you have type B antibodies.  If you are type B you have type A antibodies.  If you are type AB, you have no antibodies.  If you are type O, you have both the A and the B antibody. 

Agglutination

You never, EVER want the antigens on your cells to come into contact with the antibody that matches them.  When this happens, the antibody and antigen bond together, creating something called agglutinationThe clumping of red blood cells when antibodies bind to their specific antigens..  It’s kinda like a million little blood clots in your blood. So, in practice, I never want to see blood clots. However, in the lab, I can use this concept to identify blood types.  I can intentionally expose a patient’s blood to different antibodies. If I see agglutination, then I know that the antibody has connected with an antigen. If I don’t see agglutination after adding an antibody to a patient’s blood, the antigen for that antibody is absent. This result indicates that the antigen does not exist. The antigen for that antibody is not present.

What’s my Blood Type?

I have 5 patients here. For each patient, you see a little tiny plate with wells in it. I filled each patient’s blood into all three of the wells. 1st I take a dropper bottle full of the a antibody and I drop it into everybody’s a well. If I see agglutination it means that the antibody I dropped in has met with its corresponding antigen. I can say that my patients have the a antigen if I see agglutination.

I take a dropper bottle full of the B antibody. Then, I drop it into the B well on everybody’s sample plate. If I see agglutination then I know that the person has the B antigen. These plates also seem to have a well for the RH antigen. The RH antigen is simply a protein. It’s inserted into the plasma membraneThe outer boundary of a cell that controls what enters and exits. of red blood cells. However, it is a separate identification system than the ABO system. It’s kind of like having dimples and frecklesSmall, flat patches of increased melanin concentration in the skin. made by different genes.  Your ABO blood type is determined separately than your Rh blood type.  Just different genes.

Maria seems to have all the antigens.  Her blood type if AB+.  Mary seems to have non of the antigens!  Is she dead?!?!? No, her blood type is O-.  See if you can determine the blood type of the other three patients.  Remember, agglutination tells you that the antigen is present.

Blood Donation

In the lab we can intentionally expose antibodies to antigens. However you never want to expose antibodies to antigens while inside your patient. So again, just a reminder that we use the idea of agglutination to identify blood. We know that we never want agglutination to happen in our patient. However, we are using agglutination in the lab to determine blood type.

Sometimes when students do the previous slide, they get everything perfectly backwards. For example, Marge’s blood type is A-. In the previous slide, some students might say B.  If that’s the case then you just have the logic completely backwards. Looking at blood donation might help you understand a little bit why you have things backwards. Another example, you might have thought Maria was O- and Mary was AB+.  Let’s see if this can help.  Or hurt.

In blood donation the general rule is that you cannot get what you do not have. Let’s apply this rule to understand who you can donate to and who you can receive from. This table only considers the ABO blood groupA classification of human blood based on the presence or absence of A and B antigens on red blood c. If you are blood type A you cannot receive from blood type B they have something you don’t have. If you are blood type A you cannot receive from blood type AB because they have something you don’t have. If you are blood type A, you can receive from blood type O. Let’s consider blood type B. They can’t receive from blood type A. They can’t receive from blood type AB. They can receive from blood type O. Using our logic, blood type AB can receive blood from anyone because you cannot get what you do not have. And blood type ohh wouldn’t be able to receive blood from any of the other blood types.

If that just made you more confused let’s do this next thing and maybe something we’ll click into place. If I am blood type A I could not donate to blood type B or O. Those blood types can’t get my a antigen. I can donate to blood type AB. If I am blood type BI cannot donate to blood type AB or O. They do not have that same B antigen that I have. But I can donate to blood type AB because I wouldn’t be giving them anything that they don’t already have. With blood donations, blood type O can donate to everybody. This is because blood type O would not be giving anybody an antigen they don’t already have. In blood donations AB can receive from everyone. This is because AB has both antigens. AB would never receive something they don’t already have.

O- is the universal donorA person with type O blood, which lacks A and B antigens and can be donated to any blood type..  O- people basically have no antigens in the red blood cells.  They could donate to anyone.  AB+ is the universal receiver.  They have everything.  When you think about blood type, you have to consider the antigens AND the antibodies.