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Jai Ganesh

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Blood Group

Blood Group

Gist

There are four main blood types: A, B, AB and O. Blood bank specialists determine your blood type based on whether you have antigen A or B on your red blood cells. They also look for a protein called the Rh factor. They classify your blood type as positive (+) if you have this protein and negative (-) if you don't.

Summary

All blood does the same thing, but not all blood is the same. Blood types classify blood so healthcare providers can determine whether one person’s blood is compatible with another’s. Blood transfusions and organ transplants depend on donors and recipients having compatible blood types. Blood types include A, B, AB and O.

What are blood types?

A blood type is a classification system that allows healthcare providers to determine whether your blood is compatible or incompatible with someone else’s blood. There are four main blood types: A, B, AB and O. Blood bank specialists determine your blood type based on whether you have antigen A or B on your red blood cells. They also look for a protein called the Rh factor. They classify your blood type as positive (+) if you have this protein and negative (-) if you don’t.

This makes for eight common blood types:

* A positive (A+).
* A negative (A-).
* B positive (B+).
* B negative (B-).
* AB positive (AB+).
* AB negative (AB-).
* O positive (O+).
* O negative (O-).

Knowing about blood types allows healthcare providers to safely transfuse donated blood from one person into another during a blood transfusion. Blood types also need to be compatible for organ transplants.

How do blood types get determined?

Blood bank specialists determine blood types based on whether there are particular antigens on your red blood cells. An antigen is a substance that can make your body’s immune system react. Think of an antigen as a marker (like a nametag) that identifies a substance in your body as belonging or not belonging.

Your blood type is compatible with someone else’s if your immune system recognizes the antigens in donated blood as belonging.

What blood types mean

Most people think of A, B, AB and O when they hear the phrase “blood types.” These letters classify blood types based on whether red blood cells have the A antigen or B antigen. This is called the ABO system.

* Type A: Red blood cells have the A antigen.
* Type B: Red blood cells have the B antigen.
* Type AB: Red blood cells have both A and B antigens.
* Type O: Red blood cells have neither A nor B antigens.

Blood types are either “positive” or “negative,” depending on the absence or presence of the Rh factor’s D antigen, another marker. This is called the Rh system. Being RhD positive is more common than being RhD negative.

* Positive (+): Red blood cells have the RhD antigen.
* Negative (-): Red blood cells don’t have the RhD antigen.

Details

There are 4 main blood groups (types of blood) – A, B, AB and O. Your blood group is determined by the genes you inherit from your parents.

Each group can be either RhD positive or RhD negative, which means in total there are 8 blood groups.

Antibodies and antigens

Blood is made up of red blood cells, white blood cells and platelets in a liquid called plasma. Your blood group is identified by antibodies and antigens in the blood.

Antibodies are proteins found in plasma. They're part of your body's natural defences. 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 system

There are 4 main blood groups defined by the ABO system:

* blood group A – has A antigens on the red blood cells with anti-B antibodies in the plasma
* blood group B – has B antigens with anti-A antibodies in the plasma
* blood group O – has no antigens, but both anti-A and anti-B antibodies in the plasma
* blood group AB – has both A and B antigens, but no antibodies

Blood group O is the most common blood group. Almost half of the UK population (around 48%) has blood group O.

Receiving blood from the wrong ABO group can be life-threatening. For example, if someone with group B blood is given group A blood, their anti-A antibodies will attack the group A cells.

This is why group A blood must never be given to someone who has group B blood and vice versa.

As group O red blood cells do not have any A or B antigens, it can safely be given to any other group.

The Rh system

Red blood cells sometimes have another antigen, a protein known as the RhD antigen. If this is present, your blood group is RhD positive. If it's absent, your blood group is RhD negative.

This means you can be 1 of 8 blood groups:

* A RhD positive (A+)
* A RhD negative (A-)
* B RhD positive (B+)
* B RhD negative (B-)
* O RhD positive (O+)
* O RhD negative (O-)
* AB RhD positive (AB+)
* AB RhD negative (AB-)

About 85% of the UK population is RhD positive (35% of the population has O+, the most common type).

In most cases, O RhD negative blood (O-) can safely be given to anyone. It's often used in medical emergencies when the blood type is not immediately known.

It's safe for most recipients because it does not have any A, B or RhD antigens on the surface of the cells, and is compatible with every other ABO and RhD blood group.

Blood group test

To find out yourblood group, a sample of your blood has to be taken and tested. However, GPs do not routinely check people's blood group.

You can find out your blood group by giving blood.

For the blood group test, your red blood cells are mixed with different antibody solutions. If, for example, the solution contains anti-B antibodies and you have B antigens on your cells (you're blood group B), it will clump together.

If the blood does not react to any of the anti-A or anti-B antibodies, it's blood group O. A series of tests with different types of antibody can be used to identify your blood group.

If you have a blood transfusion (where blood is taken from one person and given to another) your blood will be tested against a sample of donor cells that contain ABO and RhD antigens. If there's no reaction, donor blood with the same ABO and RhD type can be used.

Additional Information

A 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, glycoproteins, 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 of an individual. As of 31 December 2023, a total of 45 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 − denoting RhD status) for suitability in blood transfusion.

Blood group systems

A complete blood type would describe each of the 45 blood groups, and an individual's blood type is one of many possible combinations of blood-group antigens. Almost always, an individual has the same blood group for life, but very rarely an individual's blood type changes through addition or suppression of an antigen in infection, malignancy, or autoimmune disease. Another more common cause of blood type change is a bone marrow transplant. Bone-marrow transplants are performed for many leukemias and lymphomas, among other diseases. If a person receives bone marrow from someone of a different ABO type (e.g., a type O patient receives a type A bone marrow), the patient's blood type should eventually become the donor's type, as the patient's hematopoietic stem cells (HSCs) are destroyed, either by ablation of the bone marrow or by the donor's T-cells. Once all the patient's original red blood cells have died, they will have been fully replaced by new cells derived from the donor HSCs. Provided the donor had a different ABO type, the new cells' surface antigens will be different from those on the surface of the patient's original red blood cells.

Some blood types are associated with inheritance of other diseases; for example, the Kell antigen is sometimes associated with McLeod syndrome. For another example, Von Willebrand disease may be more severe or apparent in people with blood type O. Certain blood types may affect susceptibility to infections. For example, people with blood type O may be less susceptible to pro-thrombotic events induced by COVID-19 or long covid. Another example being the resistance to specific malaria species seen in individuals lacking the Duffy antigen. The Duffy antigen, presumably as a result of natural selection, is less common in population groups from areas having a high incidence of malaria.

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