What Does It Mean To Have AB+ Blood Type?

You certainly heard someone somewhere saying their blood type is A or B or even AB, but did you ever thought for a second what that means? I surely did. Actually, I asked myself that several times during high school, but I only got to really understand it when I was in University.

Karl Landsteiner, in 1900, while having fun mixing blood from two different people, found out the blood agglutinated (which is the fancy word for ‘clumped’). That led him to find out 3 different blood types: A, B and O. One year later, the AB group was added to the list by two other researchers. It was later found out that Jan Janský, a Czech neurologist with a marvelous moustache, was actually the first one to classify human blood groups into 4 types: A, B, AB and O. This made possible the first successful blood transfusion in 1907, at Mount Sinai Hospital, NY.

Enough with history. Let’s try to understand what’s the difference between blood types. All red blood cells have sugars lining their cell membrane and these sugars differ between individuals. Some of them have the type A sugar, while others have the type B. A few people have both type A and type B and we call them AB, and others have neither of those sugars, so they are called O (or 0 (zero) because of obvious reasons).

Each one of us only recognizes as ‘safe’ the sugar we have in our own red blood cells. Let’s say a person has type A blood, which means the only sugar they regard as ‘safe’ is the type A sugar. That means that if he comes in contact with either type B or type AB blood, his body will recognize the type B sugar as ‘dangerous’, storming a bunch of antibodies against it, thus forming the blood clump. Type O doesn’t have any sugars, which means they can’t come in contact with any blood type except their own, however they can give blood to everyone else – they are universal red blood cell donors. On the contrary, type AB has the two different type of sugars there are (type A and B), which means they can receive blood from everyone else – they are universal red blood cells recipients.

This was the knowledge that made red blood cell transfusions possible at the beginning of the 20th century. Transfusions are now a very common and relatively risk-free procedure, thanks to the efforts of researchers like Landsteiner and Janský. But bear in mind that the ABO blood group system is only one of the systems we need to be aware of when transfusing red blood cells from one individual to another. Landsteiner, in 1937, also helped discover the Rhesus factor, another blood system we have to take into account.

Rhesus factor, also known as Rh factor, is called that because it was found in red blood cells from Rhesus macaque. Nowadays, whenever someone says Rh factor, they are probably referring to the D antigen of the Rh blood group system. Some of us have that antigen (which means they are Rh+), but some of us don’t (making us Rh-). Similarly to the ABO system, we can only come in contact with molecules our own body has. That’s why Rh+ individuals can receive Rh+ and Rh- blood, but Rh- individuals can never receive Rh+ blood because their immune system never saw a Rh factor before, thus considering it as ‘dangerous’. That’s why people say they have type AB Rh+ or B Rh-, because they are referring to both the ABO and Rh system.

Recently, researchers from the University of British Columbia were quite clever in creating a very efficient enzyme that removes type A and B sugars from blood, thus transforming type A, B or AB into type O blood. This enables a very simple way to create universal donor blood, facilitating blood transfusions even more and possibly allowing hospitals with scarce resources to transfuse blood on a regular basis.


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