Not as simple as ABO
Some patients need specially matched blood and that’s where rare donors come in
Matching blood to patient is always based on blood type, and the types that play the biggest part are the ABO (A, B, O and AB) and Rh systems (the D antigen being the most important - making the blood +ve or –ve). Most of the population can be safely transfused with blood matched for these types.But some patients need specially matched blood because they have a rare blood sub-type.
Looking at blood types
Before looking at what makes it rare, let’s look at the basis of blood types. A blood type is determined by antigens and antibodies present or absent in the blood.
Antigens are protein molecules (markers) found on the surface of red blood cells and antibodies are located in the blood plasma. Individuals have different types and combinations of these molecules, and they make up your blood type – A, B, AB or O, as well as your Rh factor. Find out more about your blood type.
Our bodies produce antibodies against the antigens we lack on our red cells, so if a patient were to receive blood that contained ‘rogue’ antigens, they would produce antibodies, which would bind to these antigens – with life-threatening consequences. This is why it is important that patients receive blood that has been matched correctly.
For most of us, matching the ABO groups is generally straightforward, however, there are antigens other than ABO on the red cells. Individuals who have antigens that are not commonly found in the general donor population are classed as ‘rare’. Others lack an antigen that most of the population has. In both cases it is difficult to find matching blood for these patients from our general stocks. This is when we need the help of our rare blood donors.
Matching rare types
When a request for rare blood is received, we search the donor database for donors with matching blood types. We also search for blood in the national frozen blood bank, but thawing and preparing this blood for use is expensive and, once thawed, it has a shelf life of only 24 hours. So, when time allows, the doctors and nurses from our clinical support teams will contact donors and ask them to attend the next convenient donation session.
The number of donors available depends on the rarity of the blood as well as many other factors.
Some donors won’t be able to donate for travel and medical reasons, and some may have already given blood recently, ruling out a further donation. Our available ‘pool’ of donors can sometimes shrink quite rapidly to only a handful of individuals.
Diversity helps matching
To try and maximise this pool, we are trying to recruit more donors from black, Asian and minority Ethnic (BAME) communities, who are currently under-represented in the donor population. The presence or absence of certain antigens and antibodies is linked to a person’s ethnic background, so if we can make the diversity of our donor pool match that of the general population, then we have a much better chance of finding suitable blood types.
For people who need repeated or large volume transfusions, it is best if the blood has the closest match of antigens and antibodies because it carries less risk of triggering an immune response in the patient (alloimmunisation). The best matches will come from donors of similar ethnic background.
We are grateful to all of our blood donors but especially those with rare blood types who regularly respond to our calls to give blood, often at very short notice. We see on a daily basis how these precious donations really can save lives. So to all of you who respond to the call for action – we thank you. It’s only with your help that we can continue to save and change lives.
Nykolette and Nicholas make a difference
Last year our doctors received a request for a pregnant patient whose blood contained an antibody to the ‘U’ antigen, which is found in at least 99 per cent of the population.
If pre-existing antibodies in a patient’s plasma (the liquid part of the blood) are exposed to the corresponding antigens on the red blood cells of the donor blood via transfusion, the patient’s antibodies bind to the antigens. This can cause a potentially fatal transfusion reaction.
Luckily, we had a donor who lacked the ‘U’ antigen. Nykolette Wallace (pictured) responded to our call and gave blood. She said, “I’ve been a blood donor for about 14 years now – ever since my science teacher at college told us about the lack of black blood donors in this country.
“Knowing that my blood is rare is really amazing, and makes me want to donate more. Like other donors, I don’t get to find out who receives my blood but knowing that I’m one of very few that can help these patients makes me feel really special.”
Saving a baby’s life
Babies can occasionally need blood transfusions whilst still in the womb (intra-uterine transfusions, IUTs), and last year we were asked to provide a series of IUTs to prevent potentially fatal anaemia in the baby. The mother had a complex combination of red cell antibodies and we needed donors that lacked the same combination of corresponding antigens. Thanks to blood donor Nicholas, the patient delivered a healthy baby boy.
Nicholas said, “As an O-negative donor, I knew that my donations were more in demand than others. However, this was the first time that I’d been personally called and asked to donate on a particular date – it all had to be carefully co-ordinated for the patient needing my blood.
“Obviously, as a blood donor you know you’re saving lives with each donation, but knowing that my blood was needed for this specific patient made me feel particularly proud to have been able to help – especially as it went to save a new life. That really is something.”