What are blood typing
If you need a blood transfusion or transplant, your doctor can use blood
typing and crossmatching to learn if your blood is compatible with donor blood
Blood typing reveals what type of blood you have. This depends on the
presence of certain antigens on your red blood cells (RBCs).
Antigens are proteins that trigger your immune system to produce antibodies. There
are four main types of blood:
- type A blood, which contains type-A antigens
- type B blood, which contains type-B antigens
- type AB blood, which contains type-A and type-B
- type O blood, which contains neither type-A nor type-B
Your blood will also be classified as Rh positive (+) or Rh negative (-),
based on the presence or absence of a particular protein on your RBCs, known as
Crossmatching is a test used to check for harmful interactions between your
blood and specific donor blood or organs. It can help your doctor predict how
your body will react to those donor materials.
are these tests used for?
Your doctor uses blood typing and crossmatching to learn if donor blood or
organs are compatible with your blood. Incompatible donor blood or organs can cause
harmful interactions. Your immune system may attack the donor material, leading
to dangerous and even fatal reactions.
Your doctor may order blood typing, crossmatching, or both if:
- you’re scheduled to receive a blood transfusion
or organ transplant
- you’re scheduled to undergo a medical procedure
where you face the risk of significant blood loss
- you have certain medical conditions, such as
severe anemia or a bleeding disorder
Your doctor may also order blood typing if you’re pregnant.
If your developing fetus has a different blood type than you, it raises their
risk of developing a type of anemia called hemolytic disease.
Blood typing helps your doctor determine what type of donor blood is
compatible with your own. Some blood types contain antibodies that trigger immune
reactions against other blood types. In general:
- if you have type A blood, you should only receive types
A or O blood
- if you have type B blood, you should only receive types
B or O blood
- if you have type AB blood, you can receive types A, B,
AB, or O blood
- if you have type O blood, you should only receive type
If you have type AB
blood, you’re known as a “universal recipient,” and can receive any ABO category
of donor blood. If you have type O blood, you’re known as a “universal
donor,” and anyone can receive type O blood. Type O blood is often used in
emergencies when there isn’t enough time to perform blood typing tests.
Crossmatching can also help reveal if specific donor blood or organs are
compatible with your own. In addition to anti-B and anti-A antibodies, other
types of antibodies may be present in your blood that negatively interact with
are these tests performed?
To perform blood typing and crossmatching, your doctor will collect a sample
of your blood to send to a laboratory for testing.
Collecting the sample
A trained health care practitioner can draw a sample of your blood at your
doctor’s office, blood bank, or other sites. They’ll use a needle to draw the
sample from one of your veins, usually on the inside of your elbow.
They’ll likely start by disinfecting the area with an antiseptic. An elastic band will be placed around
the upper part of your arm, causing your vein to swell up with blood. A needle
that they gently inserted into your vein will collect a sample of your blood in
collected enough blood, the practitioner will remove the needle and unwrap the
band from your arm. The puncture site will be cleaned, and if needed, bandaged.
Your blood sample will then be labeled and sent to a laboratory for testing.
Blood typing the sample
In the laboratory, a technician can conduct several tests to type your
They will mix some of your blood with commercially prepared anti-A and
anti-B antibodies. If your blood cells agglutinate, or clump
together, it means your blood has reacted with one of the antibodies.
Next, the technician will perform back typing. This calls for some of your
blood to be mixed with type A and type B blood. Your blood with then be checked
for signs of reaction.
Following that, the technician will perform Rh typing. This is when they mix
some of your blood with antibodies against Rh factor. Signs of any reaction
will be noted.
Crossmatching the sample
To crossmatch your blood against donor blood or organs, the technician will
mix a sample of your blood with a sample of the donor material. Again, they’ll check
for signs of reaction.
What do the test results mean?
Depending on the results of your blood typing, your blood will be classified
as type A, B, AB, or O. It will also be classified as Rh+ or Rh-. There is no
“normal” or “abnormal” blood type.
The results of your crossmatching test will help your doctor assess if it’s
safe for you to receive specific donor blood or organs.
If your blood cells clump only when mixed with:
- anti-A antibodies, you have type A blood
- anti-B antibodies, you have type B blood
- either anti-A or anti-B antibodies, you have type AB blood
If your blood cells don’t clump
when mixed with either anti-A or anti-B antibodies, you have type O blood.
If your blood cells clump only
when mixed with:
- type B blood, you have type A blood
- type A blood, you have type B blood
- type A or B blood, you have type O blood
If your blood cells don’t clump
when mixed with either type A or B blood, you have type AB blood.
If your blood cells clump when mixed with anti-Rh antibodies, you have Rh+ blood. If
they don’t clump, you have Rh- blood.
If your blood cells clump when mixed with a donor sample, the donor blood or organ is
incompatible with your blood.
What are the risks?
Blood draws are generally safe for most people, but they do pose some risks.
You may experience some discomfort or pain when the needle is inserted. You may
also develop bleeding, bruising, or infection at the puncture site.
In most cases, the potential benefits of blood typing and crossmatching
outweigh the risks. Talk to your doctor to learn more about the procedure. They
can also help you understand your test results and recommend appropriate