How do we test your blood donation?

Each time a blood donation is collected, we take blood samples for testing. These samples are subjected to rigorous safety checks back in our laboratory to ensure only healthy blood is distributed to hospitals.

These safety tests are essential and we carry them out on every single blood donation. We check your blood group and test for infections that can be passed from donor to patient through blood transfusion.

These tests are carried out mainly by computer controlled, automated machines, which accurately test all our donor samples.

Why do we test your blood donation?

Donor and patient safety is at the heart of everything we do and need to ensure the blood supply in Wales remains among the safest in the world. Blood collection is a heavily regulated activity and there are a number of safeguards in place to ensure only safe blood products are issued to hospitals.

What tests do we carry out?

As well as checking your blood group, we test every single donation for: Syphilis, Hepatitis (B, C and E), HIV and Human T-lymphotropic Virus (HTLV).

Supplementary tests are performed on some but not all donations. They are done to provide specifically tested blood for particular patients or they may be required because of a donor’s travel history and some other circumstances.

What happens to blood that does not pass all the blood tests?

Donations that fail any of our tests are destroyed. All samples which fail testing are sent to a second independent national laboratory to confirm our test results.

If the failed test indicates an infection that is likely to be significant to a donor’s health, we contact the donor to let them know what to do next.

Every unit of blood that is issued to hospitals in Wales is tested for:


Syphilis is caused by a bacterium called Treponema pallidum. It belongs to a family of infectious bacteria that cause yaws and pinta as well as syphilis. Syphilis is usually sexually transmitted and if untreated, can cause serious disease. Yaws and pinta are tropical diseases, which cause skin and joint problems. All three diseases are fully treatable with antibiotics. The tests we use to screen for syphilis look for antibodies, which are substances the body produces to fight infection. These antibodies can often be found in a person’s blood long after the infection has gone. A positive test for syphilis usually relates to an infection that has been treated, but if the test remains positive we are not able to use your blood.

Hepatitis B Virus (HBV)

This is a virus, which infects the liver. It can cause inflammation of the liver (hepatitis) and liver damage. HBV is very common in some parts of the world where it is often transmitted from mother to child at birth. Our screening test looks for a substance called Hepatitis B Surface Antigen, which is part of the ‘coat’ of the virus. Most of the donors we identify are long term carriers of the virus who feel completely well. Acute HBV infection is uncommon in blood donors. Occasionally we get a reaction because the donor has recently had an immunisation against HBV and not because infection is present.

Hepatitis C Virus (HCV)

This virus infects the liver and can cause inflammation and liver damage. It is commonly transmitted by injecting drug use as a result of sharing equipment. We have two kinds of test; a test for antibodies and a test for the virus. The test for the virus is an extra safety test and can tell us whether a donor with antibodies is infected or not. Most of the donors we identify with HCV are long-term carriers of the virus who feel completely well.

Hepatitis E Virus (HEV)

Can infect both animals and humans. HEV infection usually causes no symptoms but if it does these may be related to a mild inflammation of the liver.    Normally the virus infection will clear by itself. However, it is known that patients whose immune system is suppressed (e.g. chemotherapy or transplant patients) cannot clear the virus themselves and most will develop a persistent infection which may lead to chronic inflammation of the liver.    You will be informed if the virus is found in your donation, even though it will be short-lived infection, to advise you in case you start developing any signs of illness.

Human Immunodeficiency Virus (HIV)

This virus causes Acquired Immune Deficiency Syndrome (AIDS). Once an individual becomes infected with HIV then the virus remains in the body and can cause destruction of the immune system. It is mainly transmitted sexually, or from mother to baby, or by injecting drug use. A person who has HIV does not necessarily have AIDS. One of our tests looks for antibodies to the virus, and another looks for the virus itself.

Human T-lymphotropic Virus (HTLV)

This virus infects white blood cells called T-lymphocytes, and can rarely cause a neurological disorder called Tropical Spastic Paraparesis. It can also cause Adult T cell Lymphoma. It is relatively common in some areas of the world and is transmitted mainly from mother to child at birth and by breast-feeding. It can also be transmitted sexually. The test is for antibodies and a positive test means the individual is infected with the virus. Few infected individuals become ill and most carriers feel completely well.

Supplementary tests

Supplementary tests are carried out on some donations either because of information provided by the donor during health screening e.g. travel history, or to meet the special needs of certain patients e.g. babies. These tests may include: Malaria, Cytomegalovirus (CMV), T-cruzi testing and more detailed blood grouping.