People’s bodies work in very similar ways, but some differences between them are essential for treating diseases or even, for example, during pregnancy. This is the case with blood typing, which can affect certain bodies, especially when procedures such as blood transfusion are needed or during pregnancy. The different types of blood that people can have depend on the type of antigen present in their red blood cells. Due to evolution, there are different types of blood in humans, some compatible with others and some not so much1. Developing knowledge about blood typing and compatibility between people was one of the most important steps ever taken by modern medicine, as it allowed several other discoveries to be made from it. To better understand the blood types, the compatibility between them, and terms such as the ABO system and Rh factor, we need to talk more in depth about blood typing in particular, understand how it is done, and why it is so important to know about it.

ABO System

Discovered by the Austrian Karl Landsteiner2 in the 20th century, the ABO system is able to distinguish the presence or absence of A and B antigens in people’s blood, thus determining the four existing blood types, which are:

  • A
  • B
  • AB
  • O

These distinctions are not random. Blood type A, for example, has antibodies that attack type B blood, and the opposite is also true. Type O blood has antibodies that attack red blood cells of both type A and type B blood. Type AB does not attack either of the two types of antigens.

Rh Factor

In addition to the presence or absence of certain types of antigens in the blood, there is also the Rh factor3, which is another type of antigen present in the blood. The Rh system was also discovered by Karl Landsteiner and Wiener, after experiments carried out with animals. In this way, we can classify blood types as:

  • A Positive
  • A Negative
  • B Positive
  • B Negative
  • AB Positive
  • AB Negative
  • O Positive
  • O Negative

There are two situations where it is essential to know the Rh factor:

  • During pregnancy
  • At the time of a blood transfusion

Knowing the Rh factor of both the father and mother is extremely important during pregnancy, as a difference in the mother’s and baby’s Rh factor can end up causing fetal erythroblastosis or hemolytic disease of the newborn, which makes the mother’s body produce antibodies and attack the baby’s red blood cells. Fortunately, this disease can be prevented, but it is crucial to know the parents’ Rh factor so that treatment can be carried out. When performing a blood transfusion, it is also important to know the Rh factor of both the donor and the recipient. As we have said, each blood type reacts differently according to the antigens it contains, as well as the Rh factor. For this reason, not all blood types are compatible for donation or to receive.

How Is the Blood Typing Test Done?

The blood typing test is a common blood exam done by collecting a blood sample from an individual and taking it to a lab for analysis. A drop of blood is placed on a slide for each type of antigen. From this, it is possible to observe the presence or absence of agglutination in each one. The antibodies used are:

  • ANTI-A
  • ANTI-B
  • ANTI-D

If agglutination occurs for both ANTI-A and ANTI-B, it means the blood is AB; if there is no agglutination with either, it means the blood is type O.

Blood Compatibility

Based on blood typing tests, it is possible to know which blood types can receive transfusions from others. The scheme is as follows:

  • A Positive: Can receive blood from A Positive, A Negative, O Positive, and O Negative.
  • A Negative: Can receive blood from A Negative or O Positive.
  • B Positive: Can receive blood from B Negative, B Positive, O Negative, and O Positive.
  • B Negative: Can receive blood from B Negative and O Negative.
  • AB Positive: Can receive all blood types.
  • AB Negative: Can receive blood from A Negative, B Negative, AB Negative, and O Negative.
  • O Positive: Can receive blood from O Negative and O Positive.
  • O Negative: Can receive only its own blood type.

Even though many people think that certain types of knowledge are not necessary in their lives since science and medicine have already discovered them, it is important for everyone to understand that there are differences in people’s blood types and, above all, how these differences can directly affect us. Having knowledge about blood typing is not simply knowing about each blood type, but understanding the principles of procedures we experience throughout life, such as blood transfusion, effects of the Rh factor in pregnancy, and various types of tests we may need.