How is blood typed?

Blood typing was discovered in 1901 by the Austrian scientist Karl Landsteiner. Before this discovery, undergoing a blood transfusion could have fatal consequences. Landsteiner was awarded the Nobel Prize for his discovery as it led to the safe transfusion of blood. Before his discovery, people who needed to have a blood transfusion often feared for their lives due to the fact that no one knew whether the procedure would save a person’s life or end it.  

Due to the potentially devastating consequences of infusing incompatible blood into a recipient, hospitals and blood banks go to great lengths to process and screen blood while also keeping careful tabs on blood types taken from donors so as to ensure that the donated blood matches that of the receiver.

Besides the blood group ABO, there are a number of other systems responsible for blood typing that are noted prior to a transfusion. As mentioned, there are certain blood groups that can be transfused together, these groups are referred to as blood that is typed and crossed-matched.

The blood typing system known as ABO is grouped into categories according to the following criteria:

  • Type A having the A antigens.
  • Type B which has B antigens.
  • Type AB having both A and B antigens.
  • Type O having neither A nor B antigens.

To further this ABO grouping structure, blood types are also organised by the Rh factor, this is known as the Rhesus factor, being the most vital blood grouping system, after ABO of course.

The Rhesus factor is inherited from your parents and refers to the protein found on the surface of your red blood cells. Basically, if your blood type lacks the protein, then you are Rh negative. And on the other hand, if your blood type has the protein, you are then Rh positive.

This is explained as follows:

  • Rh-negative – If you are Rh-negative, your blood does not have the Rh antigens and you can therefore only receive blood from someone who is also Rh-negative.
  • Rh-positive – If you are Rh-positive, your blood does not have the Rh antigens and you can therefore only receive blood from someone who is also Rh-positive.

With the ABO and Rh grouping system in mind, these then make up eight blood groups:

  1. O negative – Does not have any A or B antigens or the Rh factor.
  2. O positive – Doesn’t have any A or B antigens, but it does have the Rh factor. This is one of the most common types of blood, with A positive being the other common type.
  3. A negative – Only consists of the A antigen on the surface of the red blood cells (RBCs).
  4. A positive – Consists of the A antigen on the RBCs and the Rh factor. It does not have the B antigen.
  5. B negative – Consists of the B antigen on RBCs only.
  6. B positive – Consists of the B antigen as well as the Rh factor. However, this blood type does not have the A antigen present on the RBC surface.
  7. AB negative – Consists of the A and B antigens, but not the Rh factor.
  8. AB positive – Consists of all three types of markers, being the A, B antigens and the Rh factor.

Blood donations are calculated as follows:

  • Type O was previously known as the universal blood type. It was believed that this blood type could donate blood to any other type due to the fact that it does not contain antigens. However, recent studies have shown that the blood type O negative should only be used in emergency situations when transfusing blood to someone with another blood type. Research has shown that even blood type O negative may contain antibodies that can result in severe reactions in a transfusion.
    • The type O blood group can only receive blood from their own group. This is due to the fact that if blood with antigens were to enter the bloodstream of an individual with type O, their immune system would recognise this as a threat and produce antibodies to combat these ‘foreign invaders’, rendering the transfusion useless and potentially devastating to the recipient.
  • Individuals with the blood type A can donate blood to any other individual who is also type A or type AB. However, type A can only receive from type A and type O.
  • Individuals with type B can donate to others with type B and those with type AB. However, type B can only receive blood from those with type B and type O.
  • Individuals with type AB are only able to give blood to those with type AB, however, they can receive from any type.
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