Blood Facts


Are you an A, a B, maybe an AB, or how about O? And are you a plus or minus?

Most people are familiar with the four big blood groups—A, B, AB, O—and the Rh factor: positive and negative. What most people don’t know is that there are also some 30 to 40 other blood group systems in the body, each with its own sub-system. For most patients, knowledge of their ABO Rh blood group is sufficient when being typed for a blood transfusion. For some patients who receive frequent blood transfusions to treat their disease or illness, however, knowledge of that patient’s other blood group is critical.

“When you phenotype someone, you get more specific information about all the other systems at play,” explains Zofia Salomon de Friedberg, manager of Diagnostic Services in Canadian Blood Services in Central Ontario.

“You are looking for blood group antigens or markers on those blood cells. These markers are proteins and they’re like ID cards. Proteins do certain things in your body and they interact with each other. That’s what gives you dark hair vs. blond hair or blue eyes vs. brown eyes. These proteins are determined by your genes. The same principle applies to your blood cells.”

On the surface of red blood cells, there are a vast number of these blood group antigens, most of which don’t cause any problem when a patient receives a single blood transfusion. But for patients who must receive many transfusions, these other blood group antigens can cause serious problems if a patient’s immune system recognizes these donated blood cells as foreign or incompatible and builds antibodies against them.

Transfusing a patient with incompatible blood could result in a haemolytic transfusion reaction, where the immune system reacts aggressively against donor red blood cells and attacks them, promoting a chain reaction that affects other cells and tissues within the body. This transfusion reaction can lead to low blood pressure, renal failure and even death.

“About 10 percent of patients will make antibodies to donated red blood cells or platelets, which means any transfusion these patients receive must be very precisely matched for these blood groups. The donors we would match for that patient often come from the same ethnic community,” says Salomon de Friedberg.

People from different ethnic groups generally have different distributions of certain blood groups. For example, there tends to be a higher incidence of type B blood in the Chinese and Black populations. In the Chinese population, the Rh-negative is very rare. In the Black community, the Fy(a-b-) blood group is very high at 68 percent, while this same group is very rare in Caucasians. Patients with sickle cell anemia (a disease which affects the Black community at a much higher rate) are therefore more likely to find a compatible blood donor from within their community than within the general population.

“Donating blood is about community—community giving and community strengthening. That is why we need more people from diverse ethnic backgrounds to get involved in blood donation; because at the end of the day it’s about helping those in your community who need it the most.”