Blood Safety Basics


CDC is one of the federal agencies responsible for promoting the safety of the U.S. blood supply. CDC conducts investigations and oversees surveillance of blood collections, donations, and adverse events, to understand potential risks to public health. The U.S. Food and Drug Administration (FDA) is responsible for ensuring safety of blood donations and protecting the health of the donors. Research on blood transfusion basic science, epidemiology, and clinical practices is carried out by the National Institutes of Health (NIH). Keeping the U.S. blood supply safe is also the responsibility of the blood centers and hospitals that collect and transfuse millions of units of blood each year.

Key Facts

Screening Donated Blood

donated blood

Blood donors are asked a set of standard questions prior to donating blood to assist in determining if they are in good health and free of any diseases that could be transmitted by blood transfusion. If the donor’s answers indicate they are not well or are at risk for having a disease transmissible by blood transfusion, they are not allowed to donate blood.

If the donor is eligible to donate, the donated blood is tested for blood type (ABO group) and Rh type (positive or negative). This is to make sure that patients receive blood that matches their blood type. Before transfusion, the donor and blood unit are also tested for certain additional proteins (antibodies) that may cause adverse reactions in a person receiving a blood transfusion.

All blood for transfusion is tested for evidence of certain infectious disease pathogens, such as hepatitis B and C viruses and human immunodeficiency virus (HIV). The tests used to screen donated blood are listed below:

tests used to screen donated blood
Infectious Disease Pathogen Laboratory Tests Used Frequency of Tests
Hepatitis B virus (HBV) Hepatitis B surface antigen (HBsAg) assay

Total antibody to hepatitis B core antigen (anti-HBc) assay

Nucleic acid testing for HBV

Every donation
Hepatitis C virus (HCV) Antibody to hepatitis C virus (anti-HCV) assay

Nucleic acid testing for HCV

Enzyme-Linked Immunosorbent Assay (ELISA) for HCV

Every donation
Human Immunodeficiency virus (HIV) Types 1 and 2 Antibodies to HIV-1 and HIV-2 (anti-HIV-1 and anti-HIV-2) assay

Nucleic acid testing for HIV-1

Every donation
Human T-Lymphotropic Virus Types I and II (HTLV) Antibodies to Human T-Lymphotropic Virus types I and II (Anti-HTLV-I/II) assay Every donation
Treponema pallidum (syphilis) Anti-treponemal antibody detection Every donation
West Nile virus (WNV) Nucleic acid testing for WNV Every donation
Trypanosoma cruzi (Chagas disease) Anti-T. cruzi assay All first-time donors tested
Cytomegalovirus (CMV) Anti-CMV assay Performed on some donations for special needs recipients
Babesia Nucleic acid test Babesia species and antibody for B. microti Performed on donations in Babesia-endemic regions
Bacterial Contamination Risk control strategies as specified by FDA guidance* See FDA guidance*

Adverse Reactions Associated with Blood Transfusions

The chance of having a reaction to a blood transfusion is very small. The most common adverse reactions from blood transfusions are allergic and febrile reactions, which make up over half of all adverse reactions reported. Rare but serious adverse reactions include infection caused by bacterial contamination of blood products and immune reactions due to problems in blood type matching between donor and recipient.

The following is a list of blood transfusion-associated adverse reactions that are tracked through the National Healthcare Safety Network (NHSN) Hemovigilance Module.

  • Allergic reaction
    An allergic reaction results from an interaction of an allergen in the transfused blood with preformed antibodies in the person receiving the blood transfusion. In some instances, infusion of antibodies from the donor may be involved. The reaction may present only with irritation of the skin and/or mucous membranes but can also involve serious symptoms such as difficulty breathing.
  • Acute hemolytic transfusion reaction (AHTR)
    An acute hemolytic transfusion reaction is the rapid destruction of red blood cells that occurs during, immediately after, or within 24 hours of a transfusion when a patient is given an incompatible blood type. The recipient’s body immediately begins to destroy the donated red blood cells, resulting in fever, pain, and sometimes severe complications such as kidney failure.
  • Delayed hemolytic transfusion reaction (DHTR)
    A delayed hemolytic transfusion reaction occurs when the recipient develops antibodies to red blood cell antigen(s) between 24 hours and 28 days after a transfusion. Symptoms are usually milder than in acute hemolytic transfusion reactions and may even be absent. DHTR is diagnosed with laboratory testing to detect specific antibodies.
  • Delayed serologic transfusion reaction (DSTR)
    A delayed serologic transfusion reaction occurs when a recipient develops new antibodies against red blood cells between 24 hours and 28 days after a transfusion without clinical symptoms or laboratory evidence of hemolysis. Since this is by definition a reaction with no clinical symptoms, severity of the reaction cannot be graded.
  • Febrile non-hemolytic transfusion reaction (FNHTR)
    Febrile non-hemolytic transfusion reactions are the most common reaction reported after a transfusion. FNHTR is characterized by fever and/or chills in the absence of hemolysis (breakdown of red blood cells) occurring in the patient during or up to 4 hours after a transfusion. These reactions are generally mild and respond quickly to treatment. Fever can be a symptom of a more severe reaction with more serious causes and should be fully investigated.
  • Hypotensive transfusion reaction
    A hypotensive transfusion reaction is a drop in systolic blood pressure occurring soon after a transfusion begins that responds quickly to cessation of the transfusion and supportive treatment. Hypotension also can be a symptom of a more severe reaction and should be fully investigated.
  • Post-transfusion purpura (PTP)
    Post-transfusion purpura is a rare but potentially fatal condition that occurs when a transfusion recipient develops antibodies against platelets, resulting in rapid destruction of both transfused platelets and the patient’s own platelets and a severe decline in the platelet count. PTP usually occurs 5-12 days after a transfusion and is more common in women than in men.
  • Transfusion-associated circulatory overload (TACO)
    Transfusion-associated circulatory overload occurs when the volume of blood or blood components transfused cannot be effectively processed by the recipient. TACO can occur due to an excessively high infusion rate and/or volume or due to an underlying heart or kidney condition. Symptoms may include difficulty breathing, cough, and fluid in the lungs.
  • Transfusion-related acute lung injury (TRALI)
    Transfusion-related acute lung injury is a serious but rare reaction that occurs when fluid builds up in the lungs but is not related to excessive volume of blood or blood products transfused. Symptoms include acute respiratory distress with no other explanation for lung injury, such as pneumonia or trauma, occurring within 6 hours of transfusion. The mechanism of TRALI is not well understood, but it is thought to be associated with the presence of antibodies in donor blood.
  • Transfusion-associated dyspnea (TAD)
    Transfusion-associated dyspnea is the onset of respiratory distress within 24 hours of transfusion that cannot be defined as TACO, TRALI, or an allergic reaction.
  • Transfusion-associated graft vs. host disease (TAGVHD)
    Transfusion-associated graft vs. host disease is a rare complication of transfusion that occurs when donor T-lymphocytes (the “graft”) introduced by the blood transfusion rapidly increase in number in the recipient (the “host”) and then attack the recipient’s own cells. Symptoms include fever, a characteristic rash, enlargement of the liver, and diarrhea that occur between 2 days and 6 weeks post transfusion. Though very rare, this inflammatory response is difficult to treat and often results in death.
  • Transfusion-transmitted infection (TTI)
    A transfusion-transmitted infection occurs when a bacterium, parasite, virus, or other potential pathogen is transmitted in donated blood to the transfusion recipient.