Blood groups and blood transfusions

Blood is essential for life. That's something we have known since the dawn of time. Losing a lot of blood is deadly. A few hundred years ago, we hardly knew anything about how the blood works. Back then, people thought that diseases were caused by the blood being bad or old.

It was common to treat diseases by letting some of the blood out - bloodletting. Sometimes it worked. But most of the time it made no difference. Or, the patient became even sicker - and maybe died. In time, people started wondering whether it would be possible to fill someone with new blood.

Transfer of blood - blood transfusion - was tested for the first time in the 17th century. At first they tried sheep blood. That didn't work out so well. It became obvious that humans needed human blood. But blood transfusions still didn't work very well: not until the 20th century - when it was discovered that people can have different blood types, and that blood from the donor must match the blood of the receiver.

This is how it works: About half of your blood consists of red blood cells, that carry oxygen and carbon dioxide in the blood. On their surfaces, red blood cells are coated in substances that vary a little, from person to person. These substances work as part of the blood cell's costume. The blood does its job just as well, whatever costume the cells are wearing. But if you get red blood cells in your body that look very different from your own, your immune system may react: "Invaders!

Fight them!" And your immune system will destroy the new blood. When performing a blood transfusion, we must be sure there's a match between the blood of the donor and the receiver. That's why we sort blood into different blood types, based on the surface of the red blood cells. There are several different systems for blood types. The most common one is called the ABO system.

In this system a person has blood type, A, B, AB or O. But there are other things that matter. For example, a person can be RhD-positive or RhD-negative. There's a lot to keep track of making a blood transfusion. Most of the time, you can receive blood from someone with the same blood type.

But it's not only blood types with the same letter that fit together. Some blood types can be given to people with other types. And some blood types can be received by several different types. Which blood type you have, depends on which types your parents have. Blood types are inherited.

Blood transfusions save lives all over the world. But they are used for different things in different regions. In high income countries, it's mostly the elderly who receive blood transfusions, when having surgery in the heart and circulatory system. In low and middle income countries, it's most common to give blood to pregnant women who are ill or who lose blood when giving birth... ... or to children, who have too few red blood cells due to malnutrition, or who have the infectious disease malaria.

People also commonly need blood because of accidents. Blood for transfusions comes from donors, who give blood to a blood bank, which is then used by hospitals. In many parts of the world, there's a shortage of blood. Not everyone who needs a transfusion can get one. Another problem is infections that can be spread by the blood.

Some are very serious, like HIV. To avoid that, all blood that is donated must be screened, to make sure it's free from disease. It can also be difficult to store, transport, and deliver blood, if you live in a place where the roads are poor, where there's a lack of sterile equipment, or where power cuts are frequent. So, there are quite a few problems still to solve. Even if blood transfusions work way better than they used to.

Baaaaah!