A, B, O and Rh D are not the only blood types. Here are some of the lesser-known groups and how they are screened
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Loading... - Anika White
- 24 Mar 2022
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Being part of the substantial slab of the Australian population with O positive blood running through my veins, I was recently surprised to find out I'm a little less common than I was in the '90s.
A national blood audit by Australian Red Cross Lifeblood researchers found the nation's changing ethnic make-up is mirrored in shifting proportions of blood types.
The proportion of people with O positive blood (like me) dropped a couple of per cent from 1993-94 to 2019.
Australia also saw an increase in the rates of people with B and AB positive blood, a reflection of migration from countries such as China and India, where those types are more prevalent.
Overall, our blood is becoming more positive — that's Rhesus D or RhD positive.
The national blood audit looked at the two blood groups we're most familiar with: ABO and RhD.
But these are just two of 40-odd human blood group systems.
So which others are important, and how are they changing too?
Why do blood types matter?
Red blood cells are usually depicted like dark red cough lozenges with a perfectly smooth surface.
But look closer, and there's a multitude of molecules embedded in the cell's surface, called antigens, that determine your blood type.
Antigens and antibodies: what's the difference?
Antigens are carbohydrate or proteins found on the surface of all blood cells (as well as body tissues and on surfaces of bacteria and viruses).
If someone is transfused with incompatible blood, the foreign antigens on those blood cells can trigger the recipient's immune system to produce antibodies.
Antibodies are Y-shaped proteins which recognise and latch onto antigens, should they encounter them again, which the immune system then clears away.
For instance, the A, B, AB or O part of your blood type refers to the presence (or absence) of A and B antigens.
If your blood type is A, you only have A antigens.
If it's B, you only have B antigens.
ABs have both, while those with an O blood type have neither.
It's a similar story with the positive or negative part of your blood type. Positive means your red blood cells sport an antigen called RhD. If you're negative, you don't have it.
Just as your body churns out antibodies to protect against infections, you can also make antibodies against unfamiliar blood antigens.
Then, if your immune system encounters those antigens again, it might attack and destroy them.
Transfusion reactions don't always cause massive problems but can mean symptoms like fever and low blood pressure.
If the reaction is severe enough and not treated, it can be life-threatening.
What is least likely to cause a reaction is O negative blood, which lacks A, B and RhD antigens. It's sometimes called the "universal blood type".
And for a woman who may one day have kids, it's especially important to use matched or O negative blood in a transfusion.
That's because there's a risk that antibodies generated from an incompatible blood transfusion could pass through the placenta (should she fall pregnant) and into a foetus's bloodstream.
This can cause a condition called haemolytic disease of the foetus and newborn, where the antibodies attack and destroy red blood cells, causing anaemia in the developing baby.
How blood is screened for 'clinically important' antibodies
Most blood donations in Australia go towards treating cancer and blood diseases.
And pre-transfusion, Australian transfusion requirements state blood screening must be done, especially in "females of child-bearing potential", where possible.
A little of their blood is taken to a laboratory to look for "clinically important" antibodies, ones that are most likely to cause reactions or haemolytic disease of the foetus and newborn, should the patient receive incompatible blood.
The standard technique first separates the recipient's red cells from the liquid part of their blood, called plasma, which contains antibodies.
A gloved hand drops liquid into an array of test tubes with a small amount of coloured liquid in the bottom.
Blood type screening has been around since the 1940s.(Supplied: Lifeblood)
A few drops of plasma is mixed with red cells of known blood type from other people, along with other substances, then heated to body temperature.
If a plasma/blood cocktail clumps together, that's a sign that antibodies are present and latching onto red blood cell antigens. Scientists can use the clumped blends to figure out the safest blood for the patient.
Pre-transfusion screening ascertains the familiar blood types of A, B, O and RhD status, says Robert Flower, who leads the Product Safety Research Group at Australian Red Cross Lifeblood.
The next most prevalent antibody of concern relates to what's known as the Kell blood system — specifically, an antibody against the K antigen.
"If you get blood containing the K antigen, and you have an antibody to that, there's up to a 40 per cent chance you'll have a fatal transfusion reaction," Professor Flower says.
The K antigen can also cause haemolytic disease of the foetus, so transfusion guidelines state that "females of child-bearing potential should … also receive red cells matched for K".
A whole raft of other blood group antigens is included on pre-transfusion screens too, such as MNS, Kidd and Duffy, along with other Rhesus antigens (such as C and E).
And for some, matching as many blood groups as closely as possible is particularly important.
Take, for instance, people with sickle cell disease, an inherited condition that contorts normally round red blood cells into crescents. Read More...
