Blood is the red fluid that circulates in our blood vessels, i.e.veins and arteries. The main function of blood is to act as the body’s transport system, but it also has a major role in the body’s defense against infection. There is no substitute for blood. It cannot be made or manufactured. Donors are the only source of blood for patients who need it.

One unit of blood can be separated into the following components:

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Nearly half the volume of blood consists of cells, which include red blood cells, white blood cells, and platelets. The remainder is a fluid called plasma.

Blood cells are produced in bone marrow.

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Red cells, white cells and platelets are made in the marrow of bones, especially the vertebrae, ribs, hips, skull and sternum. These essential blood cells fight infection, carry oxygen and help control bleeding.

Plasma carries blood cells.

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Plasma is the liquid portion of your blood that transports water and nutrients to your body’s tissues.

Red blood cells carry oxygen.

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Red blood cells are disc-shaped cells containing hemoglobin, which enables the cells to pick up and deliver oxygen to all parts of the body, then pick up carbon dioxide and remove it from tissues.

White cells defend the body.

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White cells are the body's primary defense against infection. They can move out of the blood stream and reach tissues to fight infection.

Blood Groups

Everyone’s blood falls into one of four groups, or types: A, B, AB or O. The type depends on the presence or absence of certain substances on red blood cells. Blood types are inherited. Another important blood antigen for transfusion is the Rh (or D) blood antigen.

According to AABB, the approximate distribution of blood types in the U.S. population (distribution is different for specific racial and ethnic groups):

O+O+ percent39%
O-O- percent9%
A+A+ percent31%
A-A- percent6%
B+B+ percent9%
B-B- percent2%
AB+AB+ percent3%
AB-AB- percent1%

Blood Group Compatibility

There are very specific ways in which blood types must be matched for a safe transfusion.
Rollover blood group to view compatibility.


Donor O
Group O can donate red blood cells to any recipients. It’s the universal donor.

O- blood is given to O- patients, and O+ or O- blood may be given to O+ patients.