Basically Everything You Need to Know About Blood Types for the USABO

Written By Vaishnavi Kolluru

This article covers pretty much everything I can think of about blood types. Enjoy!

Systems of genetic transmission

ABO

This blood group system is most commonly discussed, and it's for good reason: of all the blood type systems, it is most relevant to immune responses (it's the most immunogenic system). Thus, matching blood types for transfusions in the ABO blood system is the best approach. 

There are 4 blood types from this system: A, B, AB, and O. The genotypes making A are Ai and AA, B are Bi and BB, AB is just AB, and O is ii. Remember: i is an allele, while O is a phenotype where there is no marker. You can think of the i allele as a placeholder/blank.

The A and B alleles encode enzymes that can deposit surface glycoproteins on the red blood cells (RBCs). Alpha-1,3-N-acetylgalactosaminyltransferase, or A-transferase, deposits the A-glycoprotein (GalNAc) on RBCs; A-transferase is the enzyme encoded by the A allele. Beta-1,3-galactosyltransferase, or B-transferase, deposits the B-glycoprotein (GlcNAc) on RBCs; B-transferase is the enzyme encoded by the B allele. 

Rh Factor/D

Rh and D are the same thing. Rh+ is dominant to Rh-. D is dominant to d. They mean the same thing. Rh is the Rhesus factor because it was first isolated from rhesus monkeys. This system is also immunogenic like the ABO system, and is used to verify transfusion compatibility. (That's why you hear blood types are B+ for example; the B is from ABO, and the + is from Rh.)

Oh, look! It’s you.

MNSs

The M and N antigens are similarly inherited to A and B (except at the glycophorin A gene locus). The S and s are at a different locus though (the glycophorin B gene locus): those alleles are just related to if M is present or not at the M/N locus. If M is present, then S is present. If M is not present, then s is present. The S/s locus is also codominant. And to be clear, M, N, S, and s are all antigens on blood cells; they happen to be related to one another. This system is not considered to be that immunogenic relative to ABO or Rh.

How to test blood type

Typical classroom/lab blood type testing uses the ABO/Rh systems as these are the most immunogenic, so we'll see the most drastic results in the test using these systems. Anti-A, anti-B, and anti-D/anti-Rh antibodies are used on the blood sample. If the blood gets chunky, that means the corresponding antigen is present on the blood. It gets chunky due to the antibody-antigen reaction, indicating a positive result. Here’s a visual:

Hemolytic Disease of the Newborn

This disease happens when the baby's blood is Rh+ and the mom's blood is Rh- (baby got dad's genes which dominated mom's). The mom's and baby's blood typically first react when the placenta detaches during birth, but in theory, this harmful mixing occurring at any time can produce disease symptoms. It's important to note that this disease doesn't usually occur in the first pregnancy, as the mom doesn't get sensitized prior to the first delivery. However, once the mom is exposed to Rh+ blood in the first pregnancy, her body produces anti-Rh antibodies, which attack the next baby in the next pregnancy, if the next baby also has Rh+ blood.

RBC breakdown has a whole host of effects, and the whole bilirubin/hemoglobin/etc cycle is very complicated and interesting. I might write about it another week.

So yeah here's some more stuff:

Vaishnavi Kolluru
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