Why Blood is Needed

Why is blood important?

Blood is composed of the following living cells which support and maintain our body tissues:

  • Red blood cells, which are filled with hemoglobin and carry oxygen from our lungs to the rest of our bodies
  • White blood cells, which defend against infection
  • Platelets, which help blood to clot when injuries occur

How much blood does the body have?

The amount varies according to height and weight, but about seven percent of a person's body weight is composed of blood.

When might I need a blood transfusion?

Blood is usually transfused to replace red blood cells that carry oxygen. Various situations necessitate transfusion:

  • Blood loss due to bleeding, surgery or a medical procedure.
  • Medical conditions that prevent the body from producing new blood cells. Red blood cells normally have a life of three months, but medical conditions such as anemia, kidney disease, cancer, leukemia, chemotherapy and chronic disease may prevent the production of new blood cells. Transfusion may be necessary until the body is able to produce its own blood cells.
  • Disease or blood loss that hinder the clotting process in a patient's blood. Plasma and fresh frozen plasma transfused separately may be necessary to promote proper clotting.

What are the sources of blood for transfusion?

There are three sources of blood for transfusion:

  • Autologous donation — Autologous donation means to receive your own blood. This is normally the safest blood to receive. People of almost any age can donate for themselves, especially prior to surgery or a medical procedure. You may be able to donate for yourself, even if you are ineligible for allogenic donation. Ask your doctor if you are able to self-donate.
  • Designated donation — A designated donation is blood donated by a family member or friend.
  • Allogenic blood donation — This is blood that's available from the general blood supply and may be ordered for your needs by your doctor. Various factors, such as donation constraints due to your medical condition, urgency or lack of donors, may necessitate the use of this blood source.

Are there risks in receiving designated donor or allogenic blood?

All donors are screened and donor blood is tested, but there are still risks with any transfusion. The following are odds of infection from studies published in 1996:

  • Infection with the AIDS virus: 1 in 675,000 transfusions
  • Infection with HTLV: 1 in 640,000 transfusions
  • Infection with Hepatitis B virus: 1 in 63,000 transfusions
  • Infection with Hepatitis C virus: 1 in 100,000 transfusions

Other possible adverse reactions to a blood product include Graft versus Host Disease (GVHD). GVHD is a potentially life-threatening reaction from transfusion between blood relatives. Irradiation of the donated blood prevents this occurence, and is performed on all units of designated donor blood from blood relatives.

Severe allergic reaction to a blood product affects about 1 in 100,000 transfusions. Most allergic reactions are mild and cause a slight fever or rash.

As a precaution, women who may become pregnant should not receive a designated donation from their husband or partner, as it may be harmful to future children.

How are blood donors selected?

All potential donors must undergo a screening process before donating. Medical history, medications, travel history and blood count are reviewed in donor selection. Donated blood is typed and tested for evidence of infection before released for use. A "crossmatch," or final check, is performed with the recipients' blood prior to transfusion.

We advise all potential donors to answer screening and health questions carefully, to ensure the safety of the blood.

How is blood checked for infection?

All blood transfused must meet the donor eligibility requirements established by the State of California, the Food and Drug Administration, and the American Association of Blood Banks. All donated units of blood are tested for evidence of viral or bacterial infections transmitted by blood:

  • Hepatitis viruses B and C
  • HIV viruses
  • HTLV-I/II, rare viruses that cause diseases of the blood or nerves
  • Syphilis

 

Reviewed by health care specialists at UCSF Benioff Children's Hospital.

This information is for educational purposes only and is not intended to replace the advice of your doctor or health care provider. We encourage you to discuss with your doctor any questions or concerns you may have.