are a lifesaving treatment for many Americans. Blood transfusions are needed for many
reasons, including surgery, after accidents, and for patients with
illnesses and cancer.
Blood cannot be artificially made, so doctors rely on volunteer donations. To keep
the blood supply safe, every donation is tested for blood type and checked for infectious diseases.
What Are the Components of Blood?
All blood contains the same basic components:
red blood cells
white blood cells
But not everyone has the same blood type.
What Are the Blood Types?
Categorizing blood according to type helps prevent reactions when someone gets
a blood transfusion. Red blood cells have markers on their surface that characterize
the cell type. These markers (also called antigens) are proteins
and sugars that our bodies use to identify the blood cells as belonging in us.
The two main blood groups are ABO and Rh.
The ABO blood system has four main types:
Type A: This blood type has a marker known as A.
Type B: This blood type has a marker known as B.
Type AB: This blood type has both A and B markers.
Type O: This blood type has neither A or B markers.
Blood is further classified as being either "Rh positive" (meaning it
has Rh factor) or "Rh negative" (without Rh factor).
So, there are eight possible blood types:
O negative. This blood type doesn't have A or B markers, and
it doesn't have Rh factor.
O positive. This blood type doesn't have A or B markers, but
it does have Rh factor. O positive blood is one of the two most common blood types
(the other being A positive).
A negative. This blood type has A marker only.
A positive. This blood type has A marker and Rh factor, but not
B marker. Along with O positive, it's one of the two most common blood types.
B negative. This blood type has B marker only.
B positive. This blood type has B marker and Rh factor, but not
AB negative. This blood type has A and B markers, but not Rh
AB positive. This blood type has all three types of markers —
A, B, and Rh factor.
Having any of these markers (or none of them) doesn't make a person's blood any
healthier or stronger. It's just a genetic difference, like having green eyes instead
of blue or straight hair instead of curly.
Why Are Blood Types Important?
The immune system is
the body's protection against invaders. It can identify antigens as self
or nonself. To get a blood transfusion safely, a person's immune
system must recognize the donor cells as a match to his or her own cells. If a match
isn't recognized, the cells are rejected.
The immune system makes proteins called antibodies that act as
protectors if foreign cells enter the body. Depending on which blood type you have,
your immune system will make antibodies to react against other blood types.
If a patient gets the wrong blood type, the antibodies immediately set out to destroy
the invading cells. This aggressive, whole-body response can give someone a fever,
chills, and low blood pressure. It can even cause vital body systems — like breathing
or the kidneys — to fail.
Here's an example of how the blood type-antibody process works:
Let's say you have type A blood. Because your blood contains the A marker, it
makes B antibodies.
If B markers (found in type B or type AB blood) enter your body, your type A immune
system gets fired up against them.
This means that you can only get a transfusion from someone with A or O blood,
not from someone with B or AB blood.
In the same way, if you have the B marker, your body makes A antibodies. So as
a person with type B blood, you could get a transfusion from someone with B or O blood,
but not A or AB.
Things are a little different for people with type AB or type O blood:
If you have both A and B markers on the surface of your cells (type AB blood),
your body does not need to fight the presence of either.
This means that someone with AB blood can get a transfusion from someone with
A, B, AB, or O blood.
But if you have type O blood, your red blood cells have neither A or B markers.
Your body will have both A and B antibodies and will therefore feel the need to
defend itself against A, B, and AB blood.
A person with O blood can only get a transfusion with O blood.
Can Teens Donate Blood?
Blood transfusions are one of the most frequent lifesaving procedures hospitals
do. Every 2 seconds someone needs a blood transfusion. So there's always a need for
blood donors. One blood
donation can save up to three lives.
About 15% of blood donors are high school and college students. If you'd like to
help, contact your community blood center. It's one way to be an everyday superhero
and save lives!