Infectious Disease Testing

The American Red Cross performs laboratory tests for multiple infectious disease markers on every unit of donated blood. Tests are upgraded or replaced with more sensitive technologies as these become available. These tests include:

Chagas disease (T. cruzi) (2007)

Chagas disease is a serious, often fatal disease caused by the parasite Trypanosoma cruzi (T. cruzi). The agent is endemic in the Americas but most commonly occurs in Latin America. The test used is an enzyme-linked immunosorbent assay (ELISA) for the qualitative detection of antibodies to T. cruzi in human serum and plasma specimens. A radioimmunoprecipitation assay (RIPA) is used in confirmatory testing. Although T. cruzi may be transmitted to transfusion recipients, to date the Red Cross has not identified any recipients infected by blood components from donors who subsequently were confirmed positive.

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Hepatitis B virus (HBV) B Surface Antigen (HBsAg) (1971) and Hepatitis B Core Antibody (HBc) (1986)

HBsAg and HBV DNA are the first viral markers to circulate in an individual infected with HBV. Anti-HBc appears in the serum of individuals infected with HBV one to four weeks after the appearance of HBsAg, and at the onset of symptoms for the minority of individuals (5% or less) who develop symptoms. A chemiluminescent immunoassay (ChLIA) is used for the qualitative detection of HBsAg and anti-HBc in human serum and plasma specimens.  Specific antigen neutralization is used for HBsAg reactive confirmation; currently the Red Cross is not conducting confirmatory testing for anti-HBc. The risk of hepatitis B infection through blood transfusion is between 1 in 200,000 and 1 in 500,000¹.

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Hepatitis C virus (HCV 3.0) Antibody testing (1990) and Nucleic Acid Testing (NAT) (1999)

HCV is known to be the causative agent for most, if not all, blood-borne non-A, non-B hepatitis (NANBH). The ELISA test system used for blood donor screening is a third generation, qualitative, enzyme-linked, immunosorbent assay that detects antibodies to HCV in human serum or plasma.  A recombinant immunoblot assay (RIBA) is used for confirmation of anti-HCV reactivity.  HCV RNA detection by NAT uses transcription mediated amplification technology. NAT testing closes the window period between infection and the detection of antibody. The current risk of transfusion-transmitted HCV is 1 in 1,390,000¹.

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Human Immunodeficiency viruses, Types 1 and 2 (HIV 1,2) Antibody testing (1985) and NAT (1999)

Enzyme Immunoassay (EIA) is used for the qualitative detection of antibodies to both HIV-1 and HIV-2 in a combined test that uses human serum or plasma.  HIV-1 and HIV-2 confirmation is performed using one or a combination of tests including HIV-1 western blot, HIV-1 immunofluorescence and HIV-2 EIA; a rapid diagnostic test is used for HIV-1 and HIV-2 differentiation.  HIV RNA detection by NAT was introduced in 1999 to close the window period between infection and the detection of antibody; the Red Cross uses transcription mediated amplification as its NAT method.  The current risk of transfusion-transmission of HIV is approximately 1 in 2,000,000¹.

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Human T-Lymphotropic virus (HTLV-I/II) (1998)

HTLV-I is a human Type-C retrovirus that has been associated with neoplastic conditions and a variety of demyelinating disorders.  HTLV-II is not yet proven unequivocally to be of significant clinical concern. Qualitative antibody detection for both HTLV-I and HTLV-II in a combined test is performed with a ChLIA. The current risk of transfusion-transmitted (HTLV-1) is less than 1 in 2,000,000.

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Syphilis (Treponema pallidum) (1950's)

The test used for syphilis is a qualitative screening test that detects the presence of antibodies to Treponema pallidum. The assay is based on the principle of agglutination and pattern recognition. Confirmation is performed using another serologic test for total antibodies, an EIA, as well as a test for reagin (a protein-like substance that is present during acute infection and for several months following resolution of infection).  No cases of transfusion-transmitted syphilis have been recorded for more than 30 years.

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West Nile virus (WNV) (2003) 

WNV is a flavivirus commonly found in Africa, West Asia and the Middle East that is most commonly transmitted to humans through mosquito bites; it was first introduced in the US in 1999 and reached epidemic proportions in 2002, the same year that WNV was documented to be transmitted by blood and organs. WNV RNA is detected by NAT using the same type of assay as used for HIV-1 and HCV.  Following the introduction of blood donor screening there have been nine cases of transfusion transmission; all are due to donations having very low viral loads.  Measures are in place to reduce the risk of such transmissions from occurring in WNV epidemic areas by converting from testing donations in small pools (which is done for all HIV-1 and HCV NAT) to testing donors individually in areas of on-going epidemics.

In addition to these tests, the Red Cross tests every unit to identify the donor’s blood group (O, A, B or AB) and Rh type and screens for atypical or unusual red cell antibodies. Units tested negative for cytomegalovirus (CMV) are also available.

Reference: 1. Stramer S. Current Risks of Transfusion-Transmitted Agents- A Review Arch Pathol Lab Med. 2007; 131: 702-707.

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