How do we determine blood types? What are the tests done?

Answer 1

i'm guessing you just want to know how the lab types a patients blood, and less about what a blood type is.
to correctly determine the blood type of a patient you do the front type and the back type, for this you obtain a tube of blood from the patient (edta anticoagulant) and spin to separate plasma from the red cells.
the front type is determining what antigens are present on the patients red cells. to do this you use specific antibodies (anti-A, anti-B, and anti-D- these are purchased reagents and contain only the antibody listed) and mix with a suspension of the patients red cells. so into a labeled tube you add one drop antibody and one drop patients red cells suspension, spin in a centrifuge and then you gently shake the tube to observe for agglutination (note- this is NOT the same as coagulation). agglutination is just a network of antibodies and antigens and looks like a little red button in the clear liquid. if you observe agglutination in the front type it means that the patient has that specific antigen on their red cells. (so if you saw a red button with the anti-A reagent, but not with the anti-B or anti-D, the patient is A negative).
a back type is always performed as a double check of the front type. here you are determining what antibodies are present in the patients plasma. people with O blood have anti-B and anti-A, people with A blood only have anti-B, people with B blood have only anti-A, and AB people don't have any of these. you take a drop of patient plasma into a labeled tube and add a drop of reagent red cells (into one tube you add B reagent cells and to the other tibe you add A reagent cells). spin in centrifuge and again observe for agglutination. if agglutination is positive (red button) that means the patient has antibodies against that particular red cells antigen (if the A reagent cells agglutinated with the patients plasma that means the patient has anti-A).
this is how the blood bank technologist determines patient blood types.

Answer 2

So the blood cells, like all cells, have membranes. And like all cells, they have sort of "ID tags" in these membranes--they have unique proteins attached to the surface of the cells that make it so the body can have an immune response to invaders. These proteins are known as antigens, but I'll just call them proteins for simplicity's sake.

Well, in blood cells, there are two different proteins: protein A and protein B. So...

Type A: has protein A on the surface of all the blood cells
Type B: has protein B on the surface of all the blood cells
Type AB: has both protein A and protein B on the blood cells.
Type O: has neither protein A nor protein B on the blood cells.

But the blood plasma (the fluid that the cells are suspended in) has antibodies that sense proteins. So type A has the antibody "anti-B" which will attack cells with the B protein, and so on (Type AB has no antibodies and type O has antibodies "anti-A" and "anti-B")

If the body's antibodies sense proteins on the blood cells that aren't native to the body, it'll attack them. This generally causes clotting and can be fatal--oops. Not what the body intended.

This is why Type O is the universal donor--since it has no protein on the surface of the cell, the antibodies, which are only meant to attack specific proteins, don't find anything amiss. People who are Type AB are the universal acceptors, becuase their immune system is used to all of the proteins (they have no blood cell-related antibodies), and doesn't find anything wrong with any blood they recieve. People with type O blood can't recieve from anyone but Type O, because their body has both antibodies, and will attack anything else.

Now, it gets a little more complicated than that, because of the antibodies in the blood reacting in other ways, but basically what it comes down to is that people are always better off recieving transfusions of their own blood type, even if they will be okay (their lives can be saved) by Type O, and, in the case of AB, A or B.

The + and - come from another protein, I believe abbreviated as the RhD protein. + means you have it, - means you don't have it.

Blood tests basically involve people looking at the cells under a microscope and figuring out what proteins are present.

And that's basically it, but wikipedia has nice little charts and statistics if you're interested.

I don't quite know how they perform blood tests, but I believe it involves sticking the antibodies in and watching for agglutination (blood sort of clotting), which would indicate whether the blood naturally had those antibodies.

-meg

Answer 3

The two most common kinds of tests to determine your blood type: the ABO Test and the Rhesus (or Rh) Test.

The ABO Test classifies people's blood into one of four types: A, B, AB, or O. If your red blood cells have the A antigen, you have type A blood. If your red blood cells have the B antigen, you have type B blood. If you have neither the A nor B antigen, you have type O blood. Your plasma contains antibodies against both type A and type B blood. If your red blood cells have both the A and B antigens, you have type AB blood. Your plasma does not contain antibodies against either type A or type B blood. Blood received in a transfusion must contain antigens that are the same as the antigens on a person's own red blood cells (compatible blood). If you receive a transfusion that contains antigens different from your own (incompatible blood), the antibodies in your plasma will recognize the transfused (donor) blood as foreign and will attack and destroy the donor red blood cells. This is called a transfusion reaction, and it occurs immediately when incompatible blood is transfused. A transfusion reaction can be mild or cause a serious illness and even death.

Type O-negative blood does not have any antigens. It is called the "universal donor" type because it is compatible with any blood type. Type AB-positive blood is called the "universal recipient" type because a person who has it can receive blood of any type. Although "universal donor" and "universal recipient" types are occasionally used to classify blood in an emergency, blood type tests are always done to prevent transfusion reactions.


The Rhesus (or Rh) blood type checks for the presence or absence of the Rh antigen (also called the Rh factor). If your red blood cells contain the Rh antigen, your blood is Rh-positive. If they don't, your blood is Rh-negative. If your red blood cells contain both the A and Rh antigens, your blood type is A+. If your blood contains the B antigen but not the Rh antigen, your blood type is B-.

Rh blood type is especially important for pregnant women. A potential problem arises when a woman who has Rh-negative blood becomes pregnant with a baby that has Rh-positive blood. This is called Rh incompatibility. If the blood of an Rh-positive baby mixes with the blood of an Rh-negative woman during pregnancy or delivery, the mother's immune system produces antibodies. This antibody response is called Rh sensitization and, depending on when it occurs, can destroy the baby's red blood cells.

Rh sensitization does not usually affect the health of the baby during the pregnancy in which the sensitization occurs. However, the baby of a future pregnancy is more likely to be affected if the baby's blood type is Rh-positive. Once sensitization has occurred, the baby can develop mild to severe problems (called Rh disease, hemolytic disease of the newborn, or erythroblastosis fetalis). If untreated, complications from sensitization can, in rare cases, lead to the death of an Rh-positive baby.

An Rh test is done in early pregnancy to detect a woman's blood type. If she is Rh-negative, she can receive an antibody injection called Rh immune globulin (such as RhoGAM) that almost always prevents sensitization from occurring. Problems arising from Rh sensitization have become very rare since the Rh immune globulin injection was developed.

Answer 4

Tests- Agglutination. Antibodies in the blood react with antigens of another blood group and cause agglutination.