Blood transfusions save lives every day. Hospitals use blood transfusions to help people who are injured, having surgery, getting cancer treatments, or being treated for other diseases that affect the blood, like sickle cell anemia. In fact, about 5 million people each year in the United States get blood transfusions.

A Bit About Blood

Blood is like the body's transportation system, busy making deliveries and pickups. As blood circulates throughout the body, it delivers oxygen and nutrients to all the places they're needed.

Blood also collects waste products, such as carbon dioxide, and carries them to the organs responsible for making sure wastes leave the body.

Blood is a mixture of cells and liquid, and each component has a specific job:

• Red blood cells carry oxygen to the body's tissues and remove carbon dioxide. Red blood cells make up about 40%-45% of a person's blood and live for 120 days.
• White blood cells are part of the immune system, and its main defense against infection. White blood cells make up less than 1% of a person's blood.
• Platelets are cell fragments that help blood clot, which helps to prevent and control bleeding. They are about 5% of our blood.
• Plasma is a pale yellow liquid mixture of water, proteins, electrolytes, carbohydrates, cholesterol, hormones, and vitamins. About 55% of our blood is plasma.

The blood cells are made in the bone marrow, a spongy substance contained within many of the bones in the body. A full-grown adult has about 10 pints of blood (almost 5 liters) in his or her body.

What Is a Blood Transfusion?

A transfusion is a relatively simple medical procedure that doctors use to make up for a loss of blood — or for any part of the blood, such as red blood cells or platelets.

Transfusions are usually given through an intravenous line, a tiny tube that is inserted into a vein with a small needle. The whole procedure usually takes about 2 to 4 hours, depending on how much blood is needed.

Blood from a donor needs to match the blood type of the person receiving it. There are eight major blood types. They are:

1. O positive
2. O negative
3. A positive
4. A negative
5. B positive
6. B negative
7. AB positive
8. AB negative

In emergencies, there are exceptions to the rule that the donor's blood type must match the recipient's exactly. Blood type O negative is the only type of blood that people of all other blood types can receive, so it can be used in situations when patients need a transfusion but their blood type is unknown. Because of this, O negative donors are called "universal donors." People who have type AB blood are called "universal recipients" because they can safely receive any type of blood.

A blood transfusion usually isn't whole blood — it could be any one of the blood's components. For example, some people with cancer need blood transfusions because chemotherapy can affect how bone marrow makes new blood cells. So a transfusion of red blood cells or platelets can help.

Other people might need plasma or only certain parts of plasma. For example, people who have hemophilia, a disease that affects their blood's ability to clot, need plasma or the clotting factors contained in plasma to help their blood clot and prevent internal bleeding.

Where Does the Blood Come From?

In the United States, the blood supply used for transfusions comes from people who volunteer to donate their blood. Donors give blood at local blood banks, at community centers during blood drives, or through the American Red Cross.

When people know they are going to have an operation that might include a blood transfusion, they may choose to receive blood from one of several different places. Most patients choose to receive blood from the donated supply, but some decide to use their own blood. Providing your own blood before surgery is called autologous (pronounced: aw-tah-luh-gus) blood donation.

Another option for blood transfusions is called directed donation. This is when a family member or friend donates blood specifically to be used by a designated patient. For directed donation, the donor must have a blood type that is compatible with the recipient's. He or she must also meet all the requirements of a regular volunteer blood donor. There is no medical or scientific evidence that blood from directed donors is safer or better than blood from volunteer donors.

How Safe Is Donated Blood?

Some people worry about getting diseases from infected blood, but the United States has one of the safest blood supplies in the world. Many organizations, including community blood banks and the federal government, work hard to ensure that the blood supply is safe.

All blood donors must provide a thorough history, including recent travel, infections, medicines, and health problems. In addition, all blood donations are tested for several viruses, including HIV (the virus that causes AIDS), hepatitis B, hepatitis C, syphilis, and West Nile virus. If any of these things are found, the blood is destroyed. Because blood can be infected with bacteria as well as viruses, certain blood components are tested for contamination with bacteria as well.

The U.S. Food and Drug Administration (FDA) regulates U.S. blood banks. All blood centers must pass regular inspections in order to continue their operations.

Do People Get Sick From Transfusions?

Most people tolerate blood transfusions very well. But, like any medical procedure, there are some risks involved, including:

• Fever. Patients can experience a fever with a blood transfusion, sometimes along with chills, a headache, or nausea. These symptoms can be caused by a reaction between the recipient's immune system and immune cells in the donor blood. When this happens, doctors will stop the transfusion and give the patient fever-reducing medication. When the patient's temperature is back to normal, the transfusion can usually continue.
• Allergic reaction. Allergic reactions to blood transfusions (like hives or itching) happen because of a reaction between the recipient's immune system and proteins in the donated blood. In a few rare cases, an allergic reaction can be severe (a condition called anaphylaxis). Stopping the transfusion and giving the patient medications for allergy, including antihistamines and steroids, can treat these reactions. If the reaction is mild, the transfusion can start again. If it is more serious, doctors may have to take other measures before the patient can be given a transfusion again.
• Hemolytic reaction. The word hemolysis (pronounced: heh-mah-luh-sis) means the destruction of red blood cells. This reaction can be life threatening. It occurs when the patient's blood and the donated blood do not match. When the types don't match, the recipient's immune system attacks the red blood cells in the donated blood and destroys them. If a hemolytic reaction occurs, doctors stop the transfusion and treat the symptoms. Hemolytic reaction is very rare, though, as health care professionals take many precautions to confirm a patient's and donor's blood are compatible before giving a transfusion.

In almost every situation, the benefits of having a blood transfusion far outweigh the risks.

The Red Cross estimates that 15% of all blood donors in the United States are high school or college students. If you are eligible and wish to donate blood, contact your local blood bank or the American Red Cross for more information on what's involved. You could save someone's life.

Reviewed by: Maureen F. Edelson, MD
Date reviewed: May 2012