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Blood 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:

Blood Testing

Chagas disease (T. cruzi)
Antibody testing (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. Because rates of recipient infection from transfusion are so low, the Red Cross qualifies each donor (rather than each donation) for negativity to antiboides to T. cruzi.

Chagas disease

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Hepatitis B virus (HBV)
B Surface Antigen (HBsAg) (1971), Hepatitis B Core Antibody (HBc) (1986), and Nucleic Acid Testing (NAT) (2009)

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 adults (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; anti-HBc confirmation is done by testing each individual reactive donation sample by ultrasensitive HBV DNA detection by polymerase chain reaction (PCR, a type of NAT). HBV DNA detection by NAT for routine blood donor screening is done using transcription mediated amplification (TMA) technology; a type of NAT similar to PCR. Screening is performed in small minipools of 16 donations using a combined test that detects HBV DNA as well as HIV and HCV RNA. All TMA-reactive donations are confirmed by PCR. NAT using TMA in minipools of 16 reduces the window as compared to HBsAg detection by 4-7 days. The risk of hepatitis B infection through blood transfusion is between 1 in 200,000 and 1 in 500,0001,2.

Hepatitis B virus

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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 enzyme-linked, immunosorbent assay (ELISA) test system used for blood donor screening is a third generation, qualitative test 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 using TMA in minipools of 16 as described above, reduces the window period between infection and the detection of antibody by about 1-2 months. The current risk of transfusion-transmitted HCV is 1 in 1,390,0001.

Hepatitis C virus

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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 ChLIA test that uses human serum or plasma. HIV-1 and HIV- 2 confirmation is performed using one or a combination of tests including an HIV-1 indirect immunofluorescence assay (IFA) and HIV-2 EIA; a rapid diagnostic test is used for HIV-1 and HIV-2 differentiation. HIV-1 antibody detection includes the major HIV groups and variants including HIV-1 Group O. HIV RNA detection by NAT, using TMA in minipools of 16 (as described for HBV testing), closes the window period between infection and the detection of antibody by about 4-7 days. The current risk of transfusion-transmission of HIV is approximately 1 in 2,000,0001.

Human Immunodeficiency viruses - HIV

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Human T-Lymphotropic virus
Antibody testing (HTLV-I/II) (1988)

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-I) is less than 1 in 2,000,0003.

Human T-Lymphotropic virus

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Syphilis (Treponema pallidum)
Antibody testing (1940'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)
Antibody testing (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 HBV, HIV-1 and HCV. Following the introduction of blood donor screening there have been 11 documented cases of transfusion transmission; all are due to donations having very low viral loads and none involved donations to the Red Cross. Measures are in place to reduce the risk of such transmissions from occurring in WNV epidemic areas during epidemic time periods by converting from testing donations in minipools of 16 (as described for HBV, HIV-1 and HCV NAT) to testing donors individually.
West Nile virus

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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. Screening for antibodies to cytomegalovirus (CMV) is also available.


1 Stramer S. Current risks of transfusion-transmitted agents- A Review Arch Pathol Lab Med. 2007; 131: 702-707.

2 Zou S. et al Current Incidence and residual risk of hepatitis B infection among blood donors in the United States Transfusion 2009; 49:1609-1620.
3 Dodd R.Y. et al Current prevalence and incidence of infectious disease markers and estimated window-period risk in the American Red Cross blood donor population. Transfusion 2002; 42: 975-979.