Testing blood at the IBTS
The IBTS performs laboratory tests for multiple disease markers on every donor who attends our clinics and these tests include:
- Human Immunodeficiency Virus (HIV) types 1 & 2
- Hepatitis C Virus (HCV)
- Hepatitis B Virus (HBV)
- Hepatitis E virus (HEV)
- Syphilis (Treponema pallidum)
- Human T-Lymphotropic virus (HTLV) type I and II.
Any donor sample that is positive with any one of the tests above cannot be used for transfusion purposes and is discarded. Further testing is carried out to confirm true infection as distinct from a non-specific (false) reaction.
The IBTS also performs selective laboratory tests for certain disease markers on particular donors and these tests include Cytomegalovirus (CMV) West Nile Virus (WNV) Our testing systems are highly sensitive and specific for each disease marker even at low concentrations in donor blood samples. Each donor sample is tested individually. The testing systems are fully automated and compliant with EU regulations to produce accurate, reliable and consistent results. Serology based assays test for viral antibodies in donor blood samples which trigger a positive test reaction.
The time between initial infection and detection of antibodies is called the ‘window period’. Nuclaic Acid Amplification Testing (NAT) tests for the viral genetic material (DNA for HBV or RNA for HIV and HCV) which is present in donor blood samples before the body has started producing antibodies. All positive donors are informed if any virus is detected in their donor sample(s). However, donor samples can also test falsely positive for any viral marker. Further testing will be carried out to confirm the presence or absence of true infection in conjunciton with consultation from our medical personnel.
Humanimmunodeficiency Virus (HIV) type 1 & 2
Blood donation screening for HIV-1, the causative agent of Acquired Immune Deficiency Syndrome (AIDS) was first introduced by the IBTS with an antibody test in 1985. Many improvements have been made in testing methodologies including the addition of testing for a second HIV agent (HIV-2) in 1990. Antibodies to HIV-1 and HIV-2 are detected in human serum. A duplex nucleic acid test (NAT) was introduced for HIV-1/HCV detection in 2004 to detect HIV-1 RNA in blood donor plasma samples. NAT closes the window period between infection and detection of an antibody for those infected with HIV by about 2 weeks for donations tested individually, significantly reducing the risk of HIV transmission by transfusion. This leaves approximately 5 to 7 days when an infected donor may not be detected by blood screening. The risk of HIV-1 infection through blood transfusion has been calculated by the IBTS at about 1 in 15 million donations transfused. The detection of HIV-2 is an extremely rare event with no reported cases in the IBTS to date.
Hepatitis C Virus (HCV)
Blood donation screening for HCV was first introduced by the IBTS with an antibody test in 1991 to detect antibodies to HCV in human serum. In 1999, the Scottish National Blood Transfusion Service (SNBTS) tested donor samples for HCV using molecular techniques. In 2004, the IBTS implemented its own nucleic acid test (NAT) for HCV RNA detection in blood donor plasma samples. NAT closes the window period between infection and detection of an antibody for those infected with HCV by about 3 weeks. This leaves approximately 5 to 7 days when an infected donor may not be detected by blood screening. The risk of HCV infection through blood transfusion has been calculated by the IBTS at about 1 in 15 million donations transfused. All HCV positive donors are informed if the virus is detected in their donor sample.
Hepatitis B Virus (HBV)
Blood donation screening for HBV was first introduced by the IBTS with an antigen test (HBsAg) in 1973 followed by a separate antibody test (anti-HBcore) in 2002. A chemiluminescnet immunoassay (ChLIA) is used for the detection of both HBsAg and anti-HBcore in human serum. A triplex nucleic acid test (NAT) was introduced for HIV-1/HCV/HBV detection in 2009 to detect HBV DNA in blood donor plasma samples. NAT closes the window period between infection and detection of a HBsAg for those infected with HBV by about 2 weeks. This leaves aporoximately 16 days when an infected donor may not be detected by blood screening. NAT with enhanced sensitivity for HBV can detect low levels of HBV DNA in serologically negative samples during early stages of infection and in anti-HBcore antibody positive/HBsAg negative samples during later stages of infection. The risk of HBV infection through blood transfusion has been calculated by the IBTS at about 1 in 2 million donations transfused. All HBV positive donors are informed if the virus is detected in their donor sample.
Hepatitis E Virus (HEV)
Normally HEV infection will clear in the body by itself and the donor will be feeling fine, with no symptoms to report at clinics. However, patients with a suppressed immune system (e.g. transplant patients or chemotherapy patients) are unable to clear HEV and will most likely develop persistent infection if transmitted by a blood transfusion. Blood screening for HEV by NAT was introduced in the IBTS in January 2016.
Syphilis (Treponema pallidum)
Blood screening for syphilis was introduced by the IBTS in the 1950’s to detect the presence of antibodies to the spirochete bacterium Treponema pallidum. A positive test for syphilis can relate to recent infection (usually by sexual transmission) or infection in the past where antibodies remain in the donors blood for many years. In both instances, the blood donation cannot be used. Syphilis is fully treatable with antibiotics.
Human T Lymphotrophic Virus (HTLV)
Blood donation screening for HTLV (type I & II) was first introduced by the IBTS with an antibody test in 1996 to detect antibodies to HTLV in human serum.There are no NAT assays currently available for HTLV–I/II. HTLV-I is associated with neurological disorders (e.g. neoplastic conditions and a variety of demyelinating disorders). HTLV will remain in the body once an individual is infected even though antibodies develop and the blood donation cannot be used.
THe IBTS also tests donor blood samples for additional viruses but only in selected or affected donors. Selected blood donations are tested for the following two viruses according to patient needs and regulatory requirements:
- Cytomegalovirus (CMV)
- West Nile Virus (WNV)
Blood screening for Cytomegalovirus (CMV), a common virus, was introduced by the IBTS with an antibody test in 1996. CMV is part of the herpes family of viruses so once you are infected with CMV, it will remain inactive in your body for the rest of your life (CMV Positive status). CMV causes few symptoms in most people. CMV causes disease in the premature/newborn baby and in immunosuppressed individuals (e.g. chemotherapy patients, transplant patients). The IBTS selectively tests donors who are attending IBTS clinics for the first time or who were CMV negative at their last donation.
West Nile Virus (WNV) is an infection transmitted by the bites of mosquitoes. It can become a very serious illness in the elderly and in those with a suppressed immune system. Selective blood screening for WNV in individual samples was introduced using NAT testing by the IBTS in 2012. Screening is seasonal in nature whereby testing is performed on donors who have travelled to any WNV at risk area in the past 28 days prior to donating blood, typically from May to December each year. We test your donation to make sure that it is free from any possible infection although WNV often causes mild ‘flu like’ symptoms in donors.