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BLOOD GROUP AND RHESUS FACTOR : antibodies and antigens, most common blood types, blood donation etc.




blood type (also known as a blood group) is a classification of blood, based on the presence and absence of antibodies and inherited antigenic substances on the surface of red blood cells (RBCs). These antigens may be proteins, carbohydrates, glycoprotein or glycolipids, depending on the blood group system. Some of these antigens are also present on the surface of other types of cells of various tissues. Several of these red blood cell surface antigens can stem from one allele  (or an alternative version of a gene) and collectively form a blood group system.

Blood types are inherited and represent contributions from both parents. As of 2019, a total of 41 human blood group systems are recognized by the international society of blood transfusion  (ISBT) The two most important blood group systems are ABO and Rh: they determine someone’s blood type (A, B, AB, and O, with +, − or null denoting RhD status) for suitability in blood transfusion.


Blood is made up of red blood cells, white blood cells and platelets in liquid called plasma. Antibodies and antigens in the blood identify your blood group.

Antibodies are proteins found in plasma. They’re part of your body’s natural defenses. They recognise foreign substances, such as germs, and alert your immune system, which destroys them.

Antigens are protein molecules found on the surface of red blood cells.


The ABO blood group system classifies blood types according to the different types of antigens in the red blood cells and antibodies in the plasma.

They use the ABO system alongside the RhD antigen status to determine which blood type or types will match for a safe red blood cell transfusion.

There are four ABO groups:

Group A: The surface of the red blood cells contains A antigen, and the plasma has anti-B antibody. Anti-B antibody would attack blood cells that contain B antigen.

Group B: The surface of the red blood cells contains B antigen, and the plasma has anti-A antibody. Anti-A antibody would attack blood cells that contain A antigen.

Group AB: The red blood cells have both A and B antigens, but the plasma does not contain anti-A or anti-B antibodies. Individuals with type AB can receive any ABO blood type.

Group O: The plasma contains both anti-A and anti-B antibodies, but the surface of the red blood cells does not contain any A or B antigens. Since these antigens are not present, a person with any ABO blood type can receive this type of blood.


An Austrian scientist named Karl Landsteiner discovered blood groups in 1901. Before that, doctors thought all blood was the same; so many people were dying from blood transfusions.

Now experts know that if you mix blood from two people with different blood types, the blood can clump, which may be fatal. That’s because the person receiving the transfusion has antibodies that will actually fight the cells of the donor blood, causing a toxic reaction.

In order for a blood transfusion to be safe and effective, it’s important for the donor and the recipient to have blood types that go together. People with blood group A can safely get group A blood, and people with blood group B can receive group B blood.

It’s best when a donor and recipient is an exact match and their blood goes through a process called cross matching. But the donor doesn’t always need to have the exact same type of blood as the person receiving it. Their types just have to be compatible.


Deciding which type of blood is suitable (compatible) for a person who needs blood depends on the ABO group and Rh group and how they match up. If you have blood that is type:

  • A positive: You can receive donor blood that is A positive, A negative, O positive, or O negative.
  • A negative: You can receive donor blood that is A negative or O negative.
  • B positive: You can receive donor blood that is B positive, B negative, O positive or O negative.
  • B negative: You can receive donor blood that is B negative or O negative.
  • AB positive: You can receive any blood type—you are a universal recipient.
  • AB negative: You can receive donor blood that is AB negative, A negative, B negative or O negative.
  • O positive: You can receive donor blood that is O positive or O negative.
  • O negative: You can only receive donor blood that is O negative.

Note that this refers to blood and not plasma. The guidelines are different for plasma.

What is Rh factor?

Rh factor, also called Rhesus factor, is a type of protein found on the outside of red blood cells. The protein is genetically inherited (passed down from your parents). If you have the protein, you are Rh-positive. If you did not inherit the protein, you are Rh-negative. The majority of people, about 85%, are Rh-positive.

Why is Rh factor important?

This protein does not affect your overall health, but it is important to know your Rh status if you are pregnant. Rh factor can cause complications during pregnancy if you are Rh-negative and your child is Rh-positive.