Blood isn't everyone's favorite topic. In fact, you'd probably feel a lot better if it just stayed inside your body where it belongs. But blood transfusions save lives every day. Hospitals need blood for people who are injured, as well as for patients having heart surgery, organ transplants, cancer treatments, and treatments 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 the 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% to 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 clot, which helps to prevent and control bleeding. They are about 5% of our blood.
• Plasma is a yellowish 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 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.

To avoid a life-threatening reaction, blood from a donor needs to match the blood type of the person receiving it. There are eight major blood types. They are:

• O positive (about 38% of the U.S. population has this type)
• O negative (about 7 % of the U.S. population)
• A positive (about 34% of the U.S. population)
• A negative (about 6% of the U.S. population)
• B positive (about 9% of the U.S. population)
• B negative (about 2% of the U.S. population)
• AB positive (about 3% of the U.S. population)
• AB negative (only about 1% of the U.S. population)

In emergencies, there are certain 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. This is helpful in emergency situations when the patient needs 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 during chemotherapy the bone marrow may be temporarily unable to make new blood cells. For these people, 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 at local blood banks, at community centers during blood drives, or through the American Red Cross. Many people's lives depend on others being willing to donate blood.

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 volunteer blood donors. But some decide to donate their own blood before the surgery. This 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.

Who Can Donate Blood?

To donate blood, the American Red Cross requires that people be at least 17 years old and weigh more than 110 pounds. Donors must be in good health and will be screened for certain medical conditions, such as anemia. Donors who meet these requirements can give blood every 56 days.

People who meet the eligibility requirements will need to give their medical history and pass a physical exam before donating. The medical history includes questions that help blood bank staff decide if there's a risk that donors might have an infection that could be transmitted in their blood.

Are There Any Risks?

A person can't get an infection or disease from giving blood. The needles and other equipment used are sterile and they're used only on one person and then thrown away.

There are virtually no health risks associated with donating blood, according to the American Association of Blood Banks. A few donors may feel a little lightheaded, dizzy, faint, or nauseated right after giving blood. But this feeling typically goes away quickly.

The donor's body usually replaces the liquid part of blood (plasma) within 72 hours after giving blood. It generally takes about 4–8 weeks to regenerate the red blood cells lost during a blood donation. An iron-fortified diet plus daily iron tablets can help rebuild a donor's red blood supply.

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 a few risks involved. These include the following:

• Fever. Patients often get 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 they can begin the transfusion again.
• Hemolytic reaction. The word hemolysis (prononounced: 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 17 or older 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: September 2006
Originally reviewed by: Elana Pearl Ben-Joseph, MD