People receive blood transfusions for many reasons — such as surgery, injury, disease and bleeding disorders.

Blood has several components, including:

• Red cells carry oxygen and help remove waste products
• White cells help your body fight infections
• Plasma is the liquid part of your blood
• Platelets help your blood clot properly

A transfusion provides the part or parts of blood you need, with red blood cells being the most commonly transfused. You can also receive whole blood, which contains all the parts, but whole blood transfusions aren't common.

Researchers are working on developing artificial blood. So far, no good replacement for human blood is available.

Blood transfusions are generally considered safe, but there is some risk of complications. Mild complications and rarely severe ones can occur during the transfusion or several days or more after.

More common reactions include allergic reactions, which might cause hives and itching, and fever.

Bloodborne infections

Blood banks screen donors and test donated blood to reduce the risk of transfusion-related infections, so infections, such as HIV or hepatitis B or C, are extremely rare.

Other serious reactions

Also rare, these include:

• Acute immune hemolytic reaction. Your immune system attacks the transfused red blood cells because the donor blood type is not a good match. The attacked cells release a substance into your blood that harms your kidneys.
• Delayed hemolytic reaction. Similar to an acute immune hemolytic reaction, this reaction occurs more slowly. It can take one to four weeks to notice a decrease in red blood cell levels.
• Graft-versus-host disease. In this condition, transfused white blood cells attack your bone marrow. Usually fatal, it's more likely to affect people with severely weakened immune systems, such as those being treated for leukemia or lymphoma.

Your blood will be tested before a transfusion to determine whether your blood type is A, B, AB or O and whether your blood is Rh positive or Rh negative. The donated blood used for your transfusion must be compatible with your blood type.

Tell your health care provider if you've had a reaction to a blood transfusion in the past.

Blood transfusions are usually done in a hospital, an outpatient clinic or a doctor's office. The procedure typically takes one to four hours, depending on which parts of the blood you receive and how much blood you need.

Before the procedure

In some cases, you can donate blood for yourself before elective surgery, but most transfusions involve blood donated by strangers. An identification check will ensure you receive the correct blood.

During the procedure

An intravenous (IV) line with a needle is inserted into one of your blood vessels. The donated blood that's been stored in a plastic bag enters your bloodstream through the IV. You'll be seated or lying down for the procedure, which usually takes one to four hours.

A nurse will monitor you throughout the procedure and take measures of your blood pressure, temperature and heart rate. Tell the nurse immediately if you develop:

• Fever
• Shortness of breath
• Chills
• Unusual itching
• Chest or back pain
• A sense of uneasiness

After the procedure

The needle and IV line will be removed. You might develop a bruise around the needle site, but this should go away in a few days.

Contact your health care provider if you develop shortness of breath or chest or back pain in the days immediately following a blood transfusion.

You might need further blood testing to see how your body is responding to the donor blood and to check your blood counts.

Some conditions require more than one blood transfusion.