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Blood types and doughnuts: What are blood types and why do they matter?

What’s your type?

Blood type, I mean. You may already know that you’re an “O negative” or a chirpy “B positive.” Or one of many other combinations of A, B, O positive and negative.  But what do those letters mean, why do they matter, and what does the future of blood typing hold?

I know my type-I’m O negative-which means I’m a universal blood donor-and similar to about 8 percent of the population of Australia. What does that actually mean?

Imagine for a moment you’re taking one of those Magic School Bus dives into a blood stream. You shrink down to until you’re as tall as about 1/10th the width of a human hair, and you are swept along through the blood vessels with the red blood cells that are carrying oxygen to your cells. You shrink down even further, until you are able stand on one of those cells as if you were using it as a surfboard. When you look down, you can see the individual proteins that make up the surface of the red blood cell. These proteins are like signposts, machines, gateways and scaffolding, helping the red cells maintain their saucer-like structure and do their job.

Some of these proteins are responsible for your blood type. Like all the proteins that your body makes, the ones that decide your blood type come from genes that you inherit from your parents. These particular proteins are called antigens.

Antigens are so-named because they can stimulate the body to make antibodies – so they are ANTIbody GENerating.  If your body sees unfamiliar antigens in your blood, your immune system will recognise them as invaders them and try to destroy them. 

When we talk about blood types, “A” and “B” refer to two specific antigens on the surface of your red blood cells. These letters technically describe carbohydrate “decorations” on a protein molecule. And because carbohydrates are sugars, we can use sugar decorations to demonstrate the point.  Imagine a blood cell as a doughnut.

People who have the A antigen on the outside of their red cells are type A (think of A as chocolate icing on your blood-cell doughnut).

People who have the B antigen on the outside of their cells are type B (think of B as strawberry icing on your blood cell doughnut).

People who have blood type O don’t have either type of decoration (think of an un-iced, classic doughnut).

So what about the positive and negative?  That’s another antigen, called the “Rhesus” or “D” antigen, that is completely separate from A, B and O.

Generally, people either have the D antigen (in which case they are “positive”) or they don’t (in which case they are “negative”). I like to visualise this as sprinkles on the icing of the doughnuts. Like this:

donut one

Why do we worry so much about blood types? It’s because of those antibodies we mentioned before. If you are blood type A, you will develop antibodies to the B antigen and vice versa. If someone has antibodies against a blood group antigen, and they have a transfusion that contains that antigen, the antibodies will attack and destroy the foreign red blood cells. This is not only a waste of a good blood transfusion, but the broken blood cells can overload the kidneys with iron, which can be fatal.

So now we know that matching blood types is important, and we can see why the “O negative” plain doughnut is the universal donor (there are few antigens on the surface to provoke a response), and why people with AB positive blood type can take pretty much any blood type (they are used to all the trimmings).

But it gets a bit more complicated. The ABO and rhesus blood group antigens are just the most “clinically significant” antigens, which means they are most likely to generate destructive antibodies, and therefore are super important to match in any transfusion. Apart from these, though, there are literally hundreds of different blood group antigens across 36 blood group systems. (Each system is a molecule on a red blood cell’s surface that may contain one or more antigens.)

If I needed a transfusion, since I’m O negative, you could find an ABO match for me in about in about 8% of the population in Australia. If you needed to match all the antigens in my blood, it would be much more difficult (closer to 1 in 10,000).

Going back to our doughnut analogy, the full picture of antigens on red cells look more like this:

donut two

Obtaining a perfect match between donor and patient isn’t always necessary, but for people who need regular transfusions, it’s important to match as many blood groups as we can. If we don’t, they may develop antibodies that make it harder and harder to find compatible blood as their treatment continues. For example, people with thalassemia and sickle cell anemia sometimes need many transfusions every year, for life.

Traditionally blood typing is done using antibodies. A pathologist takes a patient’s blood sample and mixes it with an antibody against a certain antigen, which means one antigen can be checked per test. You can imagine it can be very time consuming to do a full blood group test. But because blood groups are determined by your genes, we can now use genetic testing to determine many blood groups at once, which can help us solve cases where no test exists.

At the Australian Red Cross Lifeblood, one of our research groups is using the latest genetic techniques, including massively parallel sequencing, to characterise new blood group antigens. They have found a number of new blood group antigens in the last few years, and are working hard to improve our ability to quickly and accurately match blood types for all patients.


This blog was originally created for the Illinois Science Council


Dr Alison Gould

Scientific Communications Specialist

At Lifeblood, Alison works with members of the Research and Development team to share their stories of science with their colleagues, collaborators and the public. Alison trained in chemistry and biochemistry, and gained a PhD in biochemistry from the University of New South Wales. She worked as a researcher in the biotechnology industry developing and manufacturing biopharmaceuticals. She loves working with scientists from all disciplines, and helping others understand the significance of their research.

Member of the Australia Science Communicators
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Best explanation for a layperson that I've ever seen. Thankyou!

Thanks Paul! Feel free to share :)

Thanks Alison for this article. I feel I now have a much better understanding of blood types due to the dougnut analogy. Also finally understand why my wife needed an Antigen D shot when our baby was born :)

Hi Robin Thanks for dropping by, I'm glad you learned something. If you're interested in anti-D, you might enjoy one of the recent episodes of "The Recording Studio" now on ABC iview, feaeturing James Harrison, one of our very dedicated anti-D donors!

Hi Alison, I’m pretty sure I’m run of the mill O+ and thought as well as donating blood I would be able to have this confirmed? I am quite interested in genetics and blood typing in general and wondered whether other blood groups, Kell, Duffy, MNS were tested through donating and if so whether these results would be made available?

Hi Lance You're right, all our blood donors have their ABO and Rhesus type confirmed and we let you know the results. We also test all donors for extended Rh antigens (C, c, E and e) and K (Kell antigen). Selected donors may at some point be tested for some blood group antigens (Duffy – Fya and Fyb, Kidd – Jka and Jkb, M, S and s antigens). These are the common clinically relevant blood group antigens out of the over 340 antigens in 36 blood group systems that we routinely test for in blood donors. Donors aren't routinely informed of these extended and fairly technical results, but can ask for access.

On the WW2 story, my father always said he was A1 (army & war)...I'm A+ & think my mother was as well; however, I married an AB+ & had 4 daughters who are all AB+ as well...My husband was a twin (not identical) & not sure of his brother's blood group (think it's different)… It's all so interesting...!!

Thanks Laurel! I'm glad you're interested in blood groups. It sounds like your family of AB + people would make great plasma donors. Did you know that AB+ is the universal plasma donor? (It's kind of opposite to red cells).

Hi all. Even knowing "my donut" has no icing, with I love I'm very happy to know that I can help who is in need. Knowing that I'm O negative makes me feel worried about it because I've been told that I only can receive my type of blood if I need it. On the other hand I'm glad. Being the Universal type, 8% of the australian population My blood is used mostly in emergencies, because my blood "fits" everyone. Thanks for having me as a blood donor

Thanks Fernando! We're proud to have you as a donor. And don't worry, the rest of us O negs will be there for you if you ever need blood yourself.

Hello - great article so I have shared this on Facebook. I currently regularly donate my plasma as a A+ blood type and was wondering if there is a possibility that I may contract antigens as I get older, and would this make my plasma less functional for recipients? I'm 51.

Thanks Meg for your regular plasma donations! In this article we have talked about antibodies to markers on the red cell surface, which can damage the red cells in recipients. However, plasma also contains antibodies that help fight diseases, and they can be very useful. As well as being used directly in transfusions, plasma is used to make a wide range of products, many of which are antibodies (also called immunoglobulins). You can read more about the many uses of plasma and the amazing powers of immunoglobulin here: If you stay healthy, you can keep donating plasma until you're over 80. Keep up the good work :)

I loved this article!!!!!!!!! So well written and great visual. :)

During WWII my parents had blood cards for emergency donations of blood, one was listed as B3- and the other as A2+. Did the numbers indicate an antigen variant within the basic blood grouping? I have asked many medical staff over the years but no-one seems to know.

Hi Ginny What a fascinating piece of history! A2 and B3 are variants of the A and B antigens. (If we wanted to extend our analogy, the icing would be the same colour, but maybe applied with texture to it). The significance of this typing wasn't clear in the 1940's, people just knew that there were some differences. Now we know a bit more about these antigens because we can study how they are made at a genetic level.

Thanks for this great illustration. I am interested in finding out more about how blood types are passed down from parent to child. I am A neg and my husband is O pos, and all our children are O pos. On that basis I assume that I am genetically AO, and I must have given O to our children. Recently, however, I discovered that both my parents are O pos. Based on the simple genetics I know I did not think this was possible. But is it more complicated than that?

Hi Sarah Thanks for your great question. Blood types can definitely be complicated! It seems that you have a strong understanding of how most blood types are inherited. However, depending on the source of each of your family member's blood typing results, there may be some room for error. We encourage you to go through your family history with your GP and the members of your family.

Hi Sarah, My wife is B and I'm A. We have two kids, one A and one B, so we deduce my wife and I are both heterozygous - BO and AO respectively.All rhesus +.

Further to Belinda's queries regarding ANTI-D, what happens if you don't receive the injection? I am RH NEG and gave birth to a RH POS baby , and did not receive the anti-D injection Will my blood now contain antigens? Thanks, Maggie

Hi Maggie The best person to speak to about whether your blood will contain antibodies is your doctor. You may find some useful information in this brochure, specially designed for Rh neg mums.

Hi there. I've recently been told by my dr that my ferritin is low. He has put me on iron tablets (Ferro C) to raise it. A follow up blood test shows that it is still on the lower end of the recommended range despite two months of Ferro C treatment ( note I usually remember to take them every 2-3 days). My last two blood donations have yielded adequate haemoglobin levels of 143-146. The previous three averaged 155. Is there a direct relationship between ferritin and haemoglobin levels?

Hi Maurice The best person to give you specific medical advice is your doctor, and its really important to look after your iron stores! In general terms, although ferritin and haemoglobin are connected, there is not a direct link between their levels. Ferritin is your long term iron store, and haemoglobin is the available iron in your blood stream. You can think of ferritin as being like your savings account, and haemoglobin is like money in your wallet. You can still have a full wallet, even when your savings account is running low-but you can't do that forever without putting more in the bank! For more information on iron health, visit

O+ here! Thanks for the cool article - I am always being asked lots of blood donor related questions by my kids and now I can explain it quite simply to them !

Hi Alison I am O- and Kel- what does this mean for my donations. I was told that people who are R negative are usually Kel +. Am I neg neg because both my parents were 0-? Heather

Hi The Kell antigen system is quite complex, and the Kell antigen can generate destructive antibodies if given to people who are Kell -ve. Around 90% of people in Australia are Kell negative. Because you are both O- and Kell -, your blood may be used for specific patients in emergencies. Whether or not you are Kell positive or negative depends on whether your parents had Kell, and isn't related to them being O -

Hi Alison, I have A+ blood, so I have at least two, but probably many more different types of antigens hitching a ride on my blood cells. That makes me wonder if those little suckers are found elsewhere in the body on other types of cells. Also, apart from being a nuisance for those people who have clean-skin blood cells, is there any other function or role they perform? Thanks.

Hi Vic-you're absolutely right. You definitely have at least two antigens on your red cells-and it's almost certain that you have many more! Some of the blood group antigens are found on cells elsewhere in the body. We are still learning about the functions of many of them-but you can get some idea of the type of things they get up to in this very readable article by one of our scientists:

I have B Rh(D) positive with anti-c. What does that mean is doughnut terms?

Hi Sally The B, in doughnut terms, gives you pink icing. The Rh(D) positive gives you sprinkles, and the anti-c means you have developed an antibody to one of the "gourmet" toppings. So perhaps you're "pink icing with sprinkles, but no hazelnuts"

Does having Anti-c antibodies cause any health problems, can these be passed through genes? I haven't found much info on anti-c

Your doctor is the best person to answer questions about how anti-c antibodies could affect your individual health. These antibodies are not passed on through genes-but develop after someone has been exposed to "c" antigen.

Hi Sally The B, in doughnut terms, gives you pink icing. The Rh(D) positive gives you sprinkles, and the anti-c means you have developed an antibody to one of the "gourmet" toppings. So perhaps you're "pink icing with sprinkles, but no hazelnuts"

An excellent article - great explanations. One question - I'm HPA positive (Human platelet antigen??). This used to be a big thing, but it seems not as important now. I give platelets and plasma Any ideas what the HPA thing means? Just curious

Thanks for your question Charlie, and it's fantastic to hear that you donate both plasma AND platelets. Platelets have many different markers on their surface just like red cells do. These markers are known as Human Platelet Antigens, and for some patients who receive platelets (especially those who have frequent transfusions or have developed antibodies to certain platelet antigens) it's important to match these as closely as possible.

I'm an A-neg, and on the antiD program. Is each boost I get the sprinkles? Or is it jam filling? Or do you extract the sprinkles from my plasma? Let's take this analogy all the way...

Thanks Pete! What a fun question :) To take the analogy all the way, each boost you get is a bunch of donuts with sprinkles (or red cells with D antigen on them). And then, because your body is a sprinkle-free zone (being D negative), it tries to get rid of the sprinkles by making a bunch of sprinkle-mopping antibodies (and if you've ever made fairy bread with a three-year-old, I bet you wish you had some of those in real life). Then we extract the "sprinkle mops" from your plasma and use them to clean up any stray sprinkles in a mum's blood that may have spilled from her baby, before her body feels the need to make its own.

Perfection. Thank you.

What a great analogy, I’m definitely going to share it. The thing that confused me in the analogy is the “extracting the sprinklemops from your plasma and use them to mop up any stray sprinkles in a mum’s body. So does the antiD consist of plain sprinkle mops? E.g. I needed AntiD in both my legs pregnancies and I’m now back to donating plasma. So your post refers to the donated and treated plasma to produce the sprinkle mops?

Thanks Victoria! anti-D is indeed "sprinklemops" that is extracted and purified from the plasma of anti-D donors. When a mum receives injections of anti-D, it does its job and is then cleared from her body, leaving her "sprinkle free" and not needing to make any of her own "sprinklemops". If she has to make her own, her body will keep up a continuous supply, which may harm a future baby. Now you are back to donating plasma (good for you!) it should be free of "sprinklemops", because you've had the benefit of borrowing some for a short time (in the form of an anti-D shot) to do a quick clean up job.

Some years ago during a donation I was told my A+ blood has an antigen which is given to premature babies. What would the antigen be?

Hi Anne It's hard to comment on the specifics of your case without more details. It may be that the nurses are referring to your blood being non-reactive for an antibody against cytomegalovirus (or CMV for short), rather than having an antigen. For people with healthy immune systems, CMV is a mild illness, possibly causing a fever and headaches. Many people wouldn’t even notice they have had the disease. However, babies who contract CMV while their brain is developing can be left with hearing loss or other permanent disabilities. To prevent infection of pregnant women and newborn babies with CMV, doctors transfuse blood from donors who have no antibodies to CMV, which indicates that they are very unlikely to have the disease.

Thanks for the question and response! This is me. I am O neg and non reactive to this antibody, helps me understand more about why I need to donate in a timely manner. I was told that my blood was in high demand due to being needed usually for new bubs and pregnant mums!

Thank you Dr. Gould for a wonderful analogy. I am a teacher and this is just brilliant. With your permission, I would like to use this in my teaching. Now I do have some question(s). Exactly when does our body develop antibodies to our antigens (ABo)? Is this in utero or after birth? If after birth does this mean a neonate can be given any blood type?

You are more than welcome to use the blog in your teaching, as long as you provide appropriate credit, attributing authorship to me and the Australian Red Cross Blood Service. You can also do this by providing a link to the website in your materials. With regards to your question, everyone is born with some blood group antibodies, and can develop others if they receive non-compatible transfusions. There are more details available at this link: Neonates most definitely cannot be given any blood type! They have some antibodies already, and they also have immune systems that function, meaning that if they receive an incompatible transfusion for which they don’t already have antibodies, they may develop them, therefore sensitising them for any future transfusions.

Happy that the blood donor service is spreading their wings I am O+ & generally donate plasma I would do it more frequently but the donor van doesn't come to the South Burnett, Qld very much, would be very great if we could have our own centre in our area. Can you tell me how to get my cholesterol back to normal & out of the red, high red blood & low white cells but only just no medication required just another blood test in 3 mths, I am going to try fish oil capsules hopefully 2000mg daily should do the trick & I like hemp oil in my smoothies, not keen of having regularly tuna & salmon I am interested in walnut & coconut oil too. Enjoy your day & I would just like to say that I love donating everybody is so nice & it's a great feeling knowing I am doing something to save lives & giving myself a health check at the same time

Hi Naomi Jennifer Thanks for being a regular donor. It's great that you are thinking about how you can improve your health. Keep up the good work, follow doctor's orders, and we look forward to seeing you next time you donate.

Excellent analogy - I have used this in my classes. Who doesn't love a doughnut! As an O-, I also encourage my students to join my Club Red 25!

I have o neg blood but have thalessaemia minor can I still donate

Thanks for your question. If you have thalassemia minor, you may be able to donate blood as long as you meet our other donation criteria. It's best to call 13 14 95 and check your eligibility.

Im rh o neg. Like plain simple things. Just like the doughnut.


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The information on this blog is presented by the Lifeblood’s Research and Development Team for the purposes of sharing general information and facilitating discussion about blood donation. It is not intended to be used or relied upon as medical advice. If you have a medical question, please consult your GP or health professional. For information on blood donation, or to find out if you’re eligible to donate, call 13 14 95.