Beth talks blood: Part 2

Blood is constantly being made by the cells inside our bone marrow. This means our bodies can usually replace any blood lost through small cuts or wounds. However, when a lot of blood is lost through larger wounds it needs to be replaces via a blood transfusion (donated by other people).

In 1628 British physician William Harvey discovers the circulation of blood, and in 1665 the first ever recorded successful blood transfusion occurred in England. Richard lower kept a dog alive through blood transfusion from other dogs [1]. It was since then that the idea of blood transfusions to save lives was a topic of interest and extensive research. It was thought that as long as the species matched, then a blood transfusion would be successful. 

However, that was not the case, if the donated blood did not match the recipient, the immune system would identify this as “non-self” and would be destroyed by antibodies, causing the transfusion to be redundant [2]. Medicine and science has come a long way since then meaning that we now know that every person has a distinct blood type. We now know that the donor-recipient blood types must be compatible in order to be accepted by the body, which is the same principle as organ transplants. Blood types are determined by genes you inherit from your parents (1 from the mother and 1 from the father) [3]. 

The four main blood types:

Group A:
Antibodies in plasma are ‘Anti-B’
Antigens on the surface of the red blood cells are ‘Antigen A’

Group B:
Antibodies in plasma ‘Anti-A’
Antigens on the surface of the red blood cells are ‘Antigen B’

Group AB:
No antibodies in plasma
Antigens for A and B on the surface of the red blood cells 

Group O:
Antibodies for A and B 
No antigens on the surface of the red blood cells

Rh factor:
Each blood type has a positive or negative component which refers to a molecule which is either present or absent on the surface of their red blood cells – it is an antigen in a blood group system called the Rh (Rhesus) system. If your red blood cells have this protein then you are Rh positive whereas if your red blood cells don’t have this protein you are Rh negative. Just as we inherited the ABO genes, every person will inherit one Rh factor gene from each parent. The Rh-positive gene is the dominant gene when paired with Rh-negative. This means there are actually 8 blood types when we include the positive or negative subcategories [2, 3, 4] .

The 8 blood types based on the Rh system:

  1. O+ (most common)
  2. A – (universal platelet type)
  3. AB+ (2% of donors)
  4. O- (universal donors)
  5. B+ (8% of donors)
  6. AB- (the rarest of the 8 blood types)
  7. A+ (second most common)
  8. B- (2% donors – very rare)

An interesting fact about people with blood type O, they are known as universal donors because they can donate blood to anyone however they can only receive blood from type O.

Have you ever donated blood? Do you know your blood type? Let me know in the comments.

Blood donations really do save lives! If you’re in the UK and you would like to donate blood please check out to see where you can donate.

Thank you for reading,

See you in the next one!

Beth x







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