Blood Bank : ABO Rh
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ABO Blood Group
The ABO blood group is determined by codominant genes (think back to intro biology!). The genes for "A" and "B" are codominant, while the "O" gene is recessive and is actually the lack of A or B. So, A and B will be expressed in the phenotype if the genes are present, while O will only be seen if neither A nor B are present. Here's a handy chart that includes possible genotypes. Notice that people with blood types (phenotypes) of A and B have TWO possible genotypes, while people with blood types of AB or O only have one possible genotype.
When a person is old enough to start making their own antibodies (not talking newborns here), they will make antibodies against whatever they don't have on their red cells. So, a type A person has "A" antigen on their RBCs. This person will make anti-B, but not anti-A. Remember, for ABO antibodies the person does NOT need prior exposure to make them, such as from a transfusion. These antibodies are naturally occurring.
Trick Question: is there an anti-O?
ABO Genes
The ABO genes do not code for the antigens themselves. But instead code for specific enzymes that add sugars to a basic precursor substance (glycoprotein or glycolipid). There is also an H gene which encodes its own specific enzyme.
RBCs have a "Type 2" precursor substance on their surface. This precursor substance is the "h" antigen. Almost all (>99.99%) people are either HH or Hh genotype. Meaning that they have the "H" gene that codes for an enzyme that puts a Fucose on the precursor chain, making an "H" antigen (h + Fucose --> H). This H antigen is what the A and B antigens are made of. The A gene calls for N acetyl-galactosamine to be put on the end of the H antigen (H + N-acetyl-galactosamine --> A), and the B gene calls for Galactose to be put on the end of the H antigen (H + Galactose --> B). If you're type O, you are just left at the H antigen stage (no upgrades for you!).
However, there are some extremely rare people who are genotype hh. Meaning, they don't make the H antigen at all. These people will forward type as a Type O person. But remember, you can make antibodies against whatever you DON'T have on your own red cells. So, these people can make anti-H! This means they will react with Type O cells (because Type O still has the H antigen). These people are called Bombay or Bombay O.
Moral of the story: if you're a Bombay O, you may want to look into autologous donations, because you can't even receive O Neg blood.
Beyond donating to the same blood type (like a Type O giving to a Type O), here's a little chart on donor compatibility:
Type O is the universal blood donor, and type AB is the universal blood receiver.
Rh Blood Group
In common terms, when someone says they are a "positive" or "negative" blood type, they're talking about the Rh group. However, it's a bit more involved than a simple pos/neg relationship.
The Rh system is composed of 5 antigens: D, C, E, c, and e.
When someone says they are positive (like, "my blood type is A Positive"), they are actually only referring to the D antigen. Of the 5 Rh antigens, D is the most immunogenic.
Tube Typing
Tube typing
Typing Discrepencies
Discrepencies
Secretor Status
Secretors
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