Blood Testing


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Tests Performed

A number of laboratory tests must be completed before blood or blood products can be transfused:

  • Determination of the blood type with a crossmatch.

  • Screening for antibodies that may produce adverse effects if transfused.

  • Screening for possible infectious agents that could be transmitted with transfusion.

The following tests are manadatory on all units of blood collected for transfusion:

  • ABO group and Rh type

  • Screening for blood-group antibodies

  • Serologic tests for human retroviruses including:

    • HIV-1

    • HIV-2

    • HTLV I

    • HTLV II

  • Serologic tests for viral hepatitis including:

    • Hepatitis B

    • Hepatitis C

  • Serologic tests for additional infectious agents including:

    • Syphilis (Treponema pallidum

    • West Nile virus

    • Chagas disease (Trypanosoma cruzi)

If, and only if, all of these markers are negative can blood be conveyed to the Blood Bank for storage until usage. A postive results for some of these tests may prevent further donation by that person. A person with such a test result will be notified by the donor center. Persons with a potential medical condition should see a physician and should not, under any circumstance, donate only to have blood tested. These measures are done to make the blood supply as safe as possible. The significant infectious diseases transmitted by transfusion and the risk of transmission (RT) in the U.S. are given below.


Transfusion Transmitted Diseases

Hepatitis B

Hepatitis B virus (HBV) is transmitted through parenteral and sexual exposure. The incubation time is a mean of 90 days with a range of 30 to 180 days.

Donor blood is routinely tested for HBsAg and HBcAb. There is no routine testing for hepatitis A, because it is rarely transmitted by blood products.

Recipients of blood products can also be infected with hepatitis delta, which is a defective RNA virus that needs a HBV superinfection to replicate.

Persons who have received a hepatitis B vaccination (recommended for all health care workers with patient contact) will have hepatitis B surface antibody present, but not HBsAg or HBcAb

Risk of transmission (RT) = 1 in 200,000 to 500,000

Hepatitis C

The route of transmission is parenteral, with sexual transmission lower than previously throught. The mean incubation time is 6 to 8 weeks.

Blood Bank testing for HCV started in 1990. At present, only testing for hepatitis C antibody is available.

Risk of transmission (RT) = 1 in 1,000,000 to 2,000,000

Human Immunodeficiency Virus (HIV)

In 1982 the first cases of AIDS obtained from blood or blood components were reported, but the etiology of the infections was not known at that time.

By 1983 changes occurred in the donor cirteria to exclude those at high risk for transmission of HIV.

The first testing of blood products for HIV started in 1985 and is a test to detect the presence of antibody directed against HIV. Testing for HIV p24 antigen was mandated in 1996.

Risk of transmission = 1 in 1,000,000 to to 2,000,000

Human T-lymphocytotrophic Virus (HTLV-I/II).

HTLV-1 is a retrovirus that is endemic in Japan and the Caribbean. Implicated as causing adult T-cell leukemia/lymphoma and a neurological disorder similar to multiple sclerosis.

Blood is routinely screened for antibodies to HTLV-I.

Risk of transmission = 1 in 2,000,000 t0 3,000,000 (but only 1-3% of seropositive individuals will develop disease).

Cytomegalovirus (CMV)

The prevalence of CMV antibody ranges from 50 to 80% of the population. Blood contaminated with CMV can cause problems in neonates or immunocompromised patients.

Potential problems in selected patient populations can be prevented by transfusing CMV negative blood or frozen, deglycerolized RBC's.

Donor blood is not routinely tested for CMV.

Malaria

Malaria is rarely transmitted by RBC products, although the number of transfusion associated cases of malaria is at an all-time high.

Donors travelling to high risk malaria areas are excluded from donating blood for six months. In areas of high prevalence, an antibody test to detect Plasmodium falciparium and Plasmodium vivax can be employed.

Bacterial Contamination

Bacterial contamination of blood can occur during collection. Bacteria can grow during storage at room temperature and during refrigeration (psychrophilic organisms). Platelet products carry the greatest risk (1 in 3000 units may have bacteria), because they are stored at room temperature. Transfusing a contaminated unit may uncommonly result in severe sepsis (1 in 100,000), septic shock and death.

Others

Additional diseases which are rarely transmitted by blood products include:

  • Lyme disease

  • Dengue fever

  • Babesiosis

  • Creutzfeldt-Jakob disease

Potential donors may be screened by questionnaire regarding travel to endemic areas or contact with persons at risk. Antibody tests available for all but babesiosis and CJD are available, preferentially applied in regions of high prevalence.


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