Tests we carry out on donated blood
You may have noticed that each time you give a blood donation we also take blood samples.
These samples are used to perform a range of screening tests in our laboratories.
Most of these tests are mandatory, in other words we must carry them out on every single blood donation, whether this is your first donation or one of the many you have given over the years.
However, there are some additional tests that may need to be done on some donations as necessary.
Sometimes the tests cannot be done, for example - if you give an incomplete blood donation or no blood samples are obtained, or if we cannot take a donation because of poor veins or you have too low a haemoglobin level for blood donation.
The tests play a very important role in ensuring that we provide a safe blood supply to patients. We test for your blood group, so that we can select the correct group for the patient.
We also test for infections that can be passed from donor to patient via a blood transfusion.
The tests are carried out by computer-controlled automated machines which can test many samples both quickly and easily, so helping us to get blood to the hospitals as fast as we can.
Any donation that is reactive on any one of the screening tests cannot be used. If your blood is reactive on any one of the screening tests, further tests are carried out to confirm whether the result indicates a true infection.
If this is the case, we will inform you and offer you appropriate advice. If the result is significant to your health you will be asked to discuss the results with one of our clinical staff and, with your permission, we will arrange a referral to your own doctor or a specialist.
If the test results show that you can no longer give blood, then you will be given specific advice.
Why do we need to test donated blood?
Donor and patient safety is at the heart of everything we do. We need to ensure the blood supply in England remains among the safest in the world.
Each donation is tested to find out the donors blood group and compared against your records if you’ve donated before. The donations are also checked for infections to help ensure that each donation is as safe as possible to transfuse to patients.
What disqualifies a person from giving blood?
Not everyone is able to give blood. To make sure the blood we give to patients is safe, we ask all donors to complete an extensive safety check questionnaire before every donation.
For safety reasons, we ask some donors never to donate, and some to wait a short while before coming back to donate.
Find out who can give blood.
What tests do we carry out when you donate blood?
- Syphilis: is caused by a bacterium called Treponema pallidum. This family of bacteria can also cause tropical diseases called Yaws and Pinta. Syphilis is usually a sexually transmitted infection which, if untreated, can cause serious disease. Yaws and Pinta cause skin and joint problems.
All three diseases are fully treatable with antibiotics. The tests we use look for specific antibodies to the bacterium. These antibodies remain in a person’s blood many years after the infection has gone.
A positive test for syphilis often relates to an infection in the past, but we are not able to use blood if the test is positive.
- Hepatitis B virus (HBV): is one of several viruses that can cause inflammation of the liver (hepatitis), and sometimes liver damage.
Hepatitis B is very common in many parts of the world where it is often transmitted from mother to child at birth or in infancy. Most donors we identify have an association with these areas of the world and appear to have been infected since childhood or in early life.
We do three tests for the virus. One looks for a marker called hepatitis B surface antigen, which is part of the ‘coat’ of the virus. The second looks for the virus itself, targeting the virus nucleic acid. The third is an anti-core screening which will identify if the donor has had Hepatitis B previously. The third test was introduced from 31 May 2022.
If we find surface antigen and/or the virus nucleic acid in a donor’s blood then further tests are performed to confirm the result. Many of the donors we identify have been infected with the virus for years and are completely well.
Sometimes we find a donor with new (acute) hepatitis B infection. Most adults who get hepatitis B have a short illness and overcome the infection.
Occasionally we get a positive result in our hepatitis B test because the donor has recently had an immunisation against hepatitis B and not because infection is present.
- Human immunodeficiency virus (HIV), if untreated, affects the immune system with the development of Acquired Immune Deficiency Syndrome (AIDS). The HIV virus is transmitted sexually, can be passed from mother to baby, and by intravenous drug use.
Once an individual becomes infected with HIV, the virus remains in the body. A person who has HIV does not necessarily have AIDS. We perform two tests for the virus; one is a combination test that looks for both a protein in the virus coat and antibody to the virus; and a second that looks for the virus itself, targeting the virus nucleic acid.
If either or both of the tests are reactive, further tests are done to confirm the result. Unlike many other infections the antibodies produced do not protect against the virus.
- Hepatitis C virus (HCV): like hepatitis B, infects the liver and can cause inflammation and liver damage. The virus is commonly transmitted by needles, and thus may be associated with injecting drug use. Like HIV, HCV can persist in the body even when antibodies are present.
We perform two tests for the virus, one that looks for antibody to the virus, and a second that looks for the virus itself, targeting the virus nucleic acid. If either or both of the tests are reactive, further tests are done to confirm the result.
Like HIV, the antibodies produced do not protect against the virus. Many of the donors we identify have had the virus for years and feel completely well.
- Hepatitis E Virus (HEV): can infect both animals and humans. HEV infection usually causes no symptoms but if it does, it generally produces only a mild inflammation of the liver, hepatitis E.
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, in case you start developing any signs of illness.
- Human T-lymphotropic virus (HTLV); a virus which infects white cells called T-lymphocytes. Like HIV, the HTLV virus remains in the body once an individual is infected, even though antibodies develop. Most people who are infected with the virus are perfectly well and never have any illness.
Occasionally, it can cause a neurological disorder called Tropical Spastic Paraparesis (or HTLV Associated Myelopathy) or a blood disease called Adult T-cell Leukaemia. These diseases are very rare.
The infection is found most commonly in people from Japan, the West Indies and parts of the Middle East. The virus is commonly transmitted from mother to child by breastfeeding, but is also passed on by sexual contact or by intravenous drug use. We screen for antibodies against HTLV, and if the test is reactive further tests are performed to confirm the result.
Some tests are not performed on every donation. We may need to carry out additional tests depending on the donor’s individual circumstances, in particular with reference to travel or skin piercing. Extra tests are also done to provide specifically tested blood for particular types of patient.
- Malaria is caused by parasites which are transmitted by the bites of mosquitoes. The infection causes fever and is a major cause of death in some parts of the world. We test for antibodies to the malaria parasites. A confirmed positive result does not necessarily mean that the individual has active malaria, merely that they have had malaria at some time.
- T-cruzi is a parasite called Trypanosoma cruzi, found in certain parts of Central and South America. It is transmitted to humans by biting insects or from mother to baby at the time of birth, or by blood transfusion.
Over many years, the parasite can cause damage to the muscles in the heart and intestines, leading to an illness called Chagas disease. Not all infected people become ill. Our tests look for antibodies to the infection. A donor’s place of birth and travel history determine whether the test is required.
- West Nile Virus (WNV) is an infection transmitted by the bites of mosquitoes. It most often causes a mild ‘flu-like’ illness, but can also cause a more serious illness, especially in the elderly and in those with a suppressed immune system. It can be transmitted by blood transfusion from a donor who has recently been infected.
WNV is commonly found in Africa, Western Asia, Europe, Australia, USA and Canada. The ‘season’ for this virus is between 1st May and 30th November.
If you have visited an area where WNV is circulating, or tell us that you have previously been diagnosed with the virus, we may test your donation to make sure that your donation is free from any possible infection. We will inform you if your test shows any sign of infection.
- Cytomegalovirus (CMV) is a very common virus which causes a mild ‘flu-like’ illness. Individuals in good health make a full recovery and are usually unaware of the infection. We may test for antibodies against the virus.
A positive test indicates that the individual has had CMV infection and may still have the virus. Having antibodies to CMV is of no significance to the health of the donor. However, for patients with a poor immune system (bone marrow recipients or small babies), CMV can cause a life-threatening illness. CMV-positive blood is safe for most patients, and donors are not informed of a positive result.
Why do we not test for other types of viruses?
We use three criteria to determine what risk an infectious disease poses to patient safety.
- Whether the infectious disease is known to (or could potentially) be transmitted by blood transfusion
- How common the disease is in our population
- How severely the infection can affect patients
We look at all the evidence and current research to work out the risk and how we should manage it. Sometimes risk factors change, so we update our rules when they do.
The quality and efficiency of our testing is very important to us, and we are regularly inspected by independent regulators to ensure we maintain our high standards.
What happens to blood that does not pass all the blood tests?
Any blood donation that reacts in our initial tests will not be used. Further tests are carried out to confirm whether the result indicates a true infection.
Any blood sample can give a reaction in laboratory screening tests, which on further testing proves to be non-specific. Non-specific reactivity can be found in all biological tests.
Whenever we obtain a reactive screen result we carry out additional testing to determine whether the reactivity is non-specific or true reactivity due to infection.
Non-specific reactivity is of absolutely no significance for the health of the donor, but unfortunately may affect the eligibility of some individuals to donate: if blood samples show such reactivity it may not be possible to use the blood. Even if you’ve given blood before without any issues, we can sometimes see unusual results in our tests. If this happens to you, you will be informed.
Our donor helpline is open for general enquiries 24 hours a day, every day of the year. If you have a non-urgent medical enquiry, please try to contact us between 9am and 5pm, Monday to Friday.