short essay on blood groups

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• Blood Groups

Blood Groups-ABO Blood Group and Rh Group System

Blood is a fluid connective tissue and the most crucial component of the circulatory system. In a healthy person, approximately 5 liters (12 pints) of blood circulates throughout their body. In this article, blood groups and their types are explained in detail.

Composition of blood is rather interesting. It consists of erythrocytes, leukocytes and platelets suspended in plasma along with the millions of different molecules with its own specific roles and functions.

Even though components of blood are the same for all humans, there are various blood types. In fact, there are more than 40 blood groups, but all of them are not clinically significant. The discovery of the ABO blood group created great excitement as until then, all blood had been assumed to be the same.

Blood Group System

Karl Landsteiner, an Austrian scientist discovered the ABO blood group system in the year 1900. In his experiments, he mixed different blood types and noted that the plasma from certain blood type produced agglutinates or formed clusters which were caused by the absence of molecules on red blood cells and resulting in antibodies to defeat that molecule. He then made a note of the agglutination and divided the blood types into 4 different groups. For the discovery of ABO blood group, he was awarded the Nobel Prize.

The blood grouping system is pivotal in blood transfusion. Our immune system recognizes another blood type as foreign and attacks it if introduced in the body causing a transfusion reaction .  Any inappropriate match with the Rh and ABO blood types, causes the most serious and life-threatening transfusion reactions. Therefore, before blood transfusion, it is suggested to have a blood group checked.

What are ABO and Rh blood groups?

During the blood transfusion, the two most important group systems examined are the ABO-system and the Rhesus system .

The ABO blood group system consists of 4 types of blood group – A, B, AB, and O and is mainly based on the antigens and antibodies on red blood cells and in the plasma. Both antigens and antibodies are protein molecules in which antigens are present on the surface of Red Blood Cells and antibodies are present in the plasma which is involved in defending mechanisms.

On the other hand, the Rh blood group system consists of 50 defined blood group antigens. In the Rh system, the most important antigens are D, C, c, E, and e. The ABO and Rh blood systems are discussed in detail below.

1. ABO blood Group system

The basis of ABO grouping is of two antigens- Antigen A and Antigen B. The ABO grouping system is classified into four types based on the presence or absence of antigens on the red blood cells surface and plasma antibodies.

• Group A – contains antigen A and antibody B.
• Group B –contains antigen B and antibody A.
• Group AB –contains both A and B antigen and no antibodies (neither A nor B).
• Group O – contains neither A nor B antigen and both antibodies A and B.

The ABO group system is important during blood donation or blood transfusion as mismatching of blood group can lead to clumping of red blood cells with various disorders. It is important for the blood cells to match while transfusing i.e. donor-recipient compatibility is necessary. For example, a person of blood group A can receive blood either from group A or O as there are no antibodies for A and O in blood group A.

As shown in the above table, individuals of blood group O are called as universal donors , whereas individuals of blood group AB are universal recipients .

2. Rh Blood Group System

In addition to the ABO blood grouping system, the other prominent one is the Rh blood group system. About two-thirds of the population contains the third antigen on the surface of their red blood cells known as Rh factor or Rh antigen ; this decides whether the blood group is positive or negative. If the Rh factor is present, an individual is rhesus positive (Rh+ve); if an Rh factor is absent individual is rhesus negative (Rh-ve) as they produce Rh antibodies. Therefore, compatibility between donor and individual is crucial in this case as well.

Frequently Asked Questions

What are blood group antigens and antibodies.

The ABO system divides blood into four major blood groups:

• Blood type A contains anti-B antibodies and A antigens in the plasma.
• Blood group B contains anti-A antibodies and B antigens in the plasma.
• Blood type O has both anti-A and anti-B antibodies in the plasma but no antigens.
• Blood type AB lacks antibodies but possesses both A and B antigens.

How are blood antibodies formed?

The immune system uses antibodies white blood cells produce to recognise and combat foreign elements in the body. Red blood cells have blood type antigens on their surface, but the immune system does not recognise them. However, antibodies will recognise the antigens of a different blood type as foreign and attack them.

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Blood Types – A, B, AB, O, Rh

Blood types are a classification of blood based on the presence or absence of specific antigens on the surface of red blood cells. These antigens determine the body’s immune response to foreign substances and are crucial in the context of blood transfusions, organ transplants, and pregnancy.

The ABO Blood Group System

The ABO blood group system is the primary blood type classification system. It categorizes blood into four main types:

• Type A: Has A antigens on the red cells and anti-B antibodies in the plasma.
• Type B: Has B antigens with anti-A antibodies in the plasma.
• Type AB: Has both A and B antigens, but no anti-A or anti-B antibodies. Known as the universal recipient.
• Type O: Has no A or B antigens, but both anti-A and anti-B antibodies. Known as the universal donor.

The Rh Factor

The Rh factor is another critical component of blood typing. It refers to the presence or absence of the Rh antigen, commonly known as the D antigen. Blood is either Rh-positive (Rh+) or Rh-negative (Rh-).

All Possible Blood Types

Combining the ABO system with the Rh factor, there are eight main blood types:

Rarest and Most Common Blood Types

The rarity of blood types varies depending on where you live. In the US:

• Rarest Blood Type: AB-, followed by B- and A-.
• Most Common Blood Type: O+, followed by A+ and B+.

Universal Donor and Receiver

• Universal Donor: O- (can be given to almost anyone, especially in emergencies).
• Universal Receiver: AB+ (can receive from all blood types).

Blood Transfusion Compatibility

• A can receive A and O
• B can receive B and O
• AB can receive A, B, AB, and O (universal recipient)
• O can receive only O (universal donor)
• Note: “Yes” indicates compatibility for a transfusion between the donor and recipient blood types.

Regarding the Rh factor, Rh+ can receive both Rh+ and Rh- blood, whereas Rh- can only receive Rh- blood.

Blood Types and Plasma Donation

The rules for plasma donation and transfusion are different from those for red blood cell transfusion because plasma contains antibodies, not antigens. Here’s how it works based on the ABO and Rh blood groups:

• AB Plasma: Universal plasma donor.
• O Plasma: Best for O recipients.
• A Plasma: Suitable for A and AB recipients.
• B Plasma: Suitable for B and AB recipients.
• T ype AB Plasma: Individuals with AB blood type are universal plasma donors because their plasma does not contain anti-A or anti-B antibodies. This means their plasma works for any recipient, regardless of the recipient’s blood type (AB, A, B, or O).
• Type O Plasma: Type O individuals, while universal red blood cell donors, are not universal plasma donors. Their plasma contains both anti-A and anti-B antibodies, which attack the red blood cells of recipients with A, B, or AB blood types. Therefore, type O plasma is only given to O recipients.
• Type A Plasma: Type A plasma can be given to recipients with type A and AB blood types, as it contains anti-B antibodies but not anti-A antibodies.
• Type B Plasma: Type B Plasma can be given to recipients with type B and AB blood types, as it contains anti-A antibodies but not anti-B antibodies.

The Rh factor (positive or negative) is less critical in plasma transfusions compared to red blood cell transfusions. This is because plasma does not typically contain Rh antibodies unless the donor has been sensitized (e.g., a woman with Rh-negative blood type who has been pregnant with an Rh-positive baby). However, in practice, compatibility is still considered to reduce any risk of reaction.

Blood Type Inheritance

Blood type inheritance is determined by the ABO and Rh genes inherited from parents. Each parent contributes one ABO allele and one Rh allele to their child.

Examples of Blood Type Inheritance

For example, if a parent has blood type A (AO genotype) and the other B (BO genotype), their child could have one of the following blood types: A (AO), B (BO), AB (AB), or O (OO). But, if one parent has blood type A (AA genotype) and the other parent has type B (BB) genotype, the blood type of a child is always AB.

Rh inheritance is separate from ABO inheritance. The Rh+ is dominant to the Rh- gene. So, an Rh+ parent has either two copies of the Rh+ gene or one, while the Rh- parent always has two copies of the Rh- gene. If one or both parents has two copies of the Rh+ gene, all children are Rh+ (even if the other parent is Rh-). Parents who are Rh- have Rh- children. If one parent has one Rh+ and one Rh- gene and the other parent is Rh-, there is a 50:50 chance for a child to be Rh+ or Rh-.

The phenotype of a person’s blood type is A, B, AB, O, Rh+, Rh- (an observable characteristic), while the genotype (e.g., AO, AB, BB) usually is unknown unless they have children or undergo genetic testing.

Rh Incompatibility and Pregnancy

Blood types play a significant role in pregnancy, primarily due to the potential for Rh incompatibility between the mother and the fetus. This occurs when an Rh-negative mother carries an Rh-positive baby. The mother’s body may recognize the baby’s Rh-positive red blood cells as foreign and produce antibodies against them. This is not usually a problem during a first pregnancy but can become an issue in subsequent pregnancies.

How Rh Incompatibility Affects Pregnancy

• Sensitization: If an Rh-negative mother is sensitized (i.e., her immune system has developed antibodies against Rh-positive blood), these antibodies cross the placenta and attack the red blood cells of an Rh-positive fetus in future pregnancies.
• Hemolytic Disease of the Newborn (HDN): This condition occurs when the mother’s antibodies destroy the fetus’s red blood cells, leading to anemia, jaundice, heart failure, and even fetal death in severe cases.

Preventing Rh Incompatibility Issues

• Rho(D) Immune Globulin (RhoGAM): Giving this medication to Rh-negative mothers during and after their first pregnancy with an Rh-positive baby prevents the mother’s immune system from becoming sensitized to Rh-positive blood cells. This protects future pregnancies.

ABO Blood Group and Pregnancy

While less common and usually less severe than Rh incompatibility, ABO incompatibility can also occur during pregnancy. This happens when the mother and baby have different ABO blood types, leading to the mother producing antibodies against the baby’s blood type. However, these antibodies are usually IgM, which do not cross the placenta, thus posing less risk to the fetus compared to the Rh incompatibility scenario.

Other Blood Type Systems

In addition to the well-known ABO and Rh blood group systems, there are several other blood group systems recognized by the International Society of Blood Transfusion (ISBT). These systems feature different sets of antigens on the surface of red blood cells. Some notable examples include:

• MNS System: This system depends on the presence or absence of M, N, S, s, and U antigens.
• Kell System: The Kell system includes antigens that are highly immunogenic, meaning they have a high potential to provoke an immune response. The most significant antigen in this system is the K antigen (also known as Kell or K1), and individuals are either K positive (K+) or K negative (K-).
• Duffy System: The Duffy system is associated with malaria resistance. The Duffy antigens (Fya and Fyb) play a role in how red blood cells interact with the parasites that cause malaria. People lacking these antigens (Fy-) are more resistant to certain types of malaria.
• Kidd System: The Kidd blood group system includes the Jka and Jkb antigens. Antibodies to these antigens cause transfusion reactions and hemolytic disease of the newborn.
• Lewis System: The Lewis blood group system is unique because Lewis antigens are not integral to the red blood cell membrane but are adsorbed onto the cell surface from plasma. Lewis antigens are involved in the body’s response to infections and are used in forensic testing.
• P System: This system includes several antigens, with the most prominent being P1. The presence or absence of these antigens is important in transfusion medicine.
• Lutheran System: The Lutheran blood group system features a large number of antigens, with Lua and Lub being the most significant. Antibodies to these antigens can cause transfusion reactions.
• Diego System: This system is important in certain populations, such as those of East Asian or Native American descent. The most notable antigens in this system are Dia and Dib.

Blood Types and Transplants

Blood groups are an important factor in organ transplants, much like in blood transfusions, but the considerations for transplantation are more complex. The compatibility of blood types between the donor and recipient is crucial for reducing the risk of transplant rejection. However, matching blood types is just one aspect of a multifaceted process. Here’s a closer look:

Blood Type Matching in Transplants

Blood groups matter in transplants, but maybe not in the way you expect:

• ABO Compatibility: Just as in blood transfusions, the ABO blood group system is critical in organ transplantation. An incompatible blood group potentially leads to immediate rejection of the transplanted organ.
• Rh Factor: Unlike in blood transfusions, the Rh factor is not a major concern in organ transplants.

Waiting Times for Transplants and Blood Groups

• Variability in Waiting Times: Some blood groups might wait longer for organ transplants due to the availability of compatible organs. For instance, Type O individuals can only receive organs from Type O donors, potentially leading to longer waiting times.
• AB Blood Group: Individuals with AB blood type often have shorter waiting times for certain transplants like kidney transplants because they can accept organs from any ABO blood group.

Beyond Blood Type Matching

Instead of matching blood groups, transplants require more comprehensive tests as well as aftercare.

• Tissue Typing (HLA Matching): Human leukocyte antigens (HLA) are proteins on the surface of cells responsible for the immune system’s recognition of self versus non-self. A closer HLA match between donor and recipient reduces the risk of organ rejection.
• Crossmatching: Before a transplant, a crossmatch test is done to ensure that the recipient’s body does not have pre-formed antibodies against the donor’s antigens, which could cause immediate organ rejection.
• Immunosuppression: Even with a good match, recipients typically need to take immunosuppressive medications for the rest of their lives to prevent rejection.

Can Your Blood Type Change?

Generally, a person’s blood type depends on genetics, so it remains constant throughout their life. However, there are very rare instances and specific medical conditions or interventions that change an individual’s blood type:

• Bone Marrow Transplant/Stem Cell Transplant: This is the most common situation where a change in blood type can occur. If a person receives a bone marrow transplant from a donor with a different blood type, the recipient’s blood type eventually changes to match the donor’s. This is because the blood cells are produced by the stem cells from the donor’s bone marrow.
• Certain Diseases or Infections: For example, there are cases where systemic lupus erythematosus (SLE) causes a temporary change in blood group, possibly due to autoantibody production.
• Blood Transfusions: In extremely rare cases and usually only in large volume transfusions, the blood type changes temporarily. This is not a true change in blood type but rather a mixing of donor and recipient blood.
• Chimerism: This rare condition occurs when an individual has two different sets of DNA, which happens as a result of a bone marrow transplant, a blood transfusion, or naturally in the case of certain types of twins. In some cases of chimerism, different parts of the body exhibit different blood types.
• Mutations: Very rare genetic mutations lead to changes in the antigens present on the surface of red blood cells, potentially altering the perceived blood type. However, such cases are extremely uncommon.
• Avent, N.D. (2009). “Large-scale blood group genotyping: clinical implications”. Br J Haematol . 144 (1): 3–13. doi :10.1111/j.1365-2141.2008.07285.x
• Fauci, Anthony S.; Braunwald, Eugene; et al. (1998). Harrison’s Principals of Internal Medicine . McGraw-Hill. ISBN 0-07-020291-5.
• Kremer Hovinga, I.; Koopmans, M.; et al. (2007). “Change in blood group in systemic lupus erythematosus”. Lancet . 369 (9557): 186–7, author reply 187. doi: 10.1016/S0140-6736(07)60099-3
• Maton, Anthea; Hopkins, Jean; et al. (1998). Human Biology and Health . Englewood Cliffs NJ: Prentice Hall. ISBN 0-13-981176-1.
• Stayboldt, C.; Rearden, A.; Lane, T.A. (1987). “B antigen acquired by normal A1 red cells exposed to a patient’s serum”. Transfusion . 27 (1): 41–4. doi: 10.1046/j.1537-2995.1987.27187121471.x

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Explainer: what are blood groups and why do they matter?

Associate Professor; Head, Transfusion Research Unit, Monash University

Clinical Research Fellow in Haematology, Monash University

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If you’ve ever needed a blood transfusion, or donated blood, you probably would have been asked your blood type. While it was once thought all blood was the same, we now know there are different types of blood, called blood groups. Transfusions between blood groups can be catastrophic, even deadly, so knowing the blood type of donors and recipients is of the utmost importance.

Our bodies contain trillions of red blood cells. Each is covered in an array of proteins and sugars, inherited from our parents, which determine our blood group. We can all be classified into group A, B, AB or O, based on which sugars coat our red blood cells.

We’re also classified as positive or negative, based on whether our blood cells carry a protein called the Rhesus D (RhD) antigen. These two blood group systems (ABO and Rh) give us the eight main blood types: O-, O+, B-, B+, A-, A+, AB-, AB+.

But there are also more than 300 different antigens – proteins and sugars that activate the immune system – expressed on red cells and 36 recognised blood group systems. And they’re just the ones we know about.

While most people know they are, for example, A+ or O-, few people will know (and never need to know) what their expression of other red cell antigens are.

How were blood groups discovered?

Transfusion has been practised intermittently since the 1660s . But blood groups weren’t discovered until 1900, before which it was assumed that all blood was of the same type.

This led to some catastrophic transfusions of animal blood into humans in attempts to transfer certain qualities (for example, so the recipient would become meek like a lamb). There were also some fatal transfusions between humans.

For this reason, the practice was banned in the UK and France for more than 100 years.

In 1900, physician Karl Landsteiner ’s experiments showed that some people’s red cells “reacted” with plasma samples from other people, while others did not. This led to him describing the ABO system, the most important blood group system and the basis of safe modern transfusion.

After receiving the 1930 Nobel Prize for Medicine for this work, Landsteiner was experimenting with the blood of Rhesus monkeys when he discovered what is now known as the RhD antigen.

Compatibility

If we need to transfuse blood from one person to another, we want to give donor blood that is compatible with the recipient’s blood to minimise the chance of a transfusion reaction.

So if a person is group A, this means she can receive a red cell transfusion from either a group A or a group O donor. She should not receive group B or AB red cells, as she has naturally occurring antibodies (proteins formed as part of the immune response) that will likely cause a transfusion reaction, which may be serious – even fatal .

Around 31% of Australians are A+. It’s the second most common blood group after O+, which make up 40% of the Australian population .

Group O negative people are called “universal donors”. Their red cells express neither group A nor B sugars, nor the RhD antigen, and so are unlikely to cause a reaction in recipients.

Emergency departments and some ambulances carry a stock of O negative blood, because in an emergency this is the safest blood to give a critically ill, bleeding patient of unknown blood type. Only 9% of the Australian population are O negative.

The Australian Red Cross Blood Service needs a diverse group of blood donors to meet the needs of our increasingly diverse patient population.

What are blood groups for?

It is likely all of the molecules that cover the surface of cells serve some purpose – often completely unrelated to transfusion.

One of the 36 blood group systems mentioned above is the Colton blood group. This is interesting because the molecules recognised by the immune system as Colton blood group antigens are actually located on an aquaporin (AQP1) molecule - one of a family of molecules responsible for water passage into and out of cells, and abundant in the red cell membrane. Professor Peter Agre and colleagues described this in 1992 and he received a Nobel Prize for this work.

Another interesting example is the Duffy protein , named after a haemophiliac patient Mr Duffy . In 1950, he developed an antibody to what we know today as the Duffy “a” antigen, to which he had been exposed by receiving a blood transfusion.

One of the known functions of the Duffy antigens is binding one type of malaria parasite, Plasmodium vivax , which grants it entry into the red cell, where it can multiply and then cause the cell to burst.

The red cells of people who lack Duffy antigens are more resistant to infection by this parasite. More than two-thirds of people of African origin lack the Duffy antigens, whereas it is rare for people originating from Europe or Asia to do so.

Many thousands of years ago, in Africa where the Plasmodium vivax -bearing mosquitoes flourished, people who lacked Duffy antigens were resistant to this potentially fatal form of malaria and survived to parent future generations, passing on this particular resilience to their offspring.

Fascinatingly, the normal function of ABO and Rh, the two most important blood group systems, is still essentially unknown. The frequency of ABO antigens varies greatly between different populations, and so it is thought that perhaps particular ABO blood types confers survival advantage in different settings.

Different ABO blood types occur more frequently in some medical conditions. Stomach ulcers, for example, are more common in those with group O blood but stomach cancer is more common in those with group A blood. We don’t really know exactly why this occurs, or its consequences.

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ABO Blood Group System

ABO blood grouping is based on the principle of an agglutination reaction . It is the popular method for blood group identification to determine the presence and absence of cellular antigens and their relative antibodies in the blood. In blood typing, the detection of antigen in the donor’s RBCs is called forward typing. In contrast, the  detection of antibodies in the donor’s plasma or serum is known as reverse typing .

According to the ABO-blood group system, A , B , AB and O are the four phenotypes. Type A and B are the two antigens associated with the RBC membrane, while anti-A and anti-B are the two antibodies naturally present in the blood plasma. The blood typing or the blood group identification is performed by the blood-test kit that contains anti-A, anti-B and anti-D antisera.

The antigens of the ABO blood group system are glycolipid in nature, and the antibodies are predominantly of IgM type. In this context, we will study the principle, method and result interpretation of the ABO blood typing. Besides, we will also discuss some of the discoveries, facts and the overview of the ABO blood group system.

Content: ABO Blood Group System

Interpretation of result, abo compatibility, meaning of abo blood group system.

The ABO blood group system has type A, B, AB and O phenotypes and it is used to identify the type of surface antigens and antibodies present in the donor’s blood. If agglutination occurs in the RBCs, then the corresponding antibody must be absent in the blood plasma. The antigens if absent on the RBCs membrane, then the corresponding antibodies must be present in the blood plasma. Individuals above 3-6 month have naturally occurring antibodies which arise without any antigenic stimulation from the maternal placenta. These antibodies belong to the IgM class. ABO blood group is also present in some other animals like gorillas, chimpanzees etc.

History of ABO Blood Grouping

According to the ABO blood group system, there are four blood groups, namely A , B , AB and O .

Method of ABO Blood Group System

• First, scrub the middle finger with cotton saturated with 70% of alcohol .
• Then, prick the middle finger by sterilized needle or lancet.
• After that, place three drops on a clean glass slide.
• Then after this, add antisera in a sequence of anti- A in a first drop, anti- B in a second drop and anti- D to the third drop, respectively.
• Mix the blood with the antisera separately by using a sterilized toothpick.
• Allow the slide to stand for 2-3 minutes and then note down the results based on clump formation or agglutination reaction.

• If the agglutination occurs in the RBCs, to which anti-A is added, then the blood group is ‘ A ’.
• When agglutination occurs in the RBCs, to which anti-B is added, then the blood group is ‘ B ’.
• If the agglutination occurs in the RBCs, to which both anti-A and B are added, then the blood group is ‘ AB ’.
• When there is no agglutination occurs in the RBCs, then the blood group is ‘ O ’.

In addition, there is also another antiserum that is anti-D , which determines the positive and negative blood type .

• If the agglutination occurs in the RBCs to which anti-D is added, then the blood type is positive (+) and if no agglutination occurs in the RBCs mixed anti-D, then the blood type is negative (-).

Theory of blood transfusion states that before transfusion, the ABO compatibility of blood type must be checked, as any carelessness can affect the immune system.

• A person with blood group A can receive blood from the person with blood types A and O.
• The person with blood group B can receive blood from the person with blood types B and O.
• A person with blood group AB can receive blood from the person with all blood types A, B, AB and O and called as Universal recipient .
• The person with blood group O can receive blood from only the person with blood type O.
• A person with blood group A can donate blood to the person with blood types A and AB.
• The person with blood group B can donate blood to the person with blood types B and AB.
• A person with blood group AB can donate blood to only the person with blood type AB.
• A person with blood group O can donate blood to the person with all blood types A, B, AB and O and hence called Universal donor .

Therefore, the ABO blood group system is one of the popular technique to classify human blood. ABO blood group system majorly classifies the blood into four types, i.e. A, B, AB and O. Agglutination reaction determines the ABO blood type, which is determined by the clump formation in the blood. ABO blood group system was accepted by the National Research Council and popularly known as Landsteiner classification .  Karl Landsteiner won the Nobel prize in the year 1930 for his contribution in this.

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Blood Types: What Letters, Positive, and Negative Signs Mean

What to Know About Your Blood Type

• Blood Types
• Why to Know Your Type
• Compatibility
• Significance in Pregnancy
• Finding Your Blood Type

Your blood type is a combination of letters and signs identifying antigens present or absent on the surface of your red blood cells. Antigens are substances that can trigger the immune system to produce antibodies. Antibodies are proteins that lead an attack on substances perceived as foreign "invaders."

Blood typing is essential if you need to receive a blood transfusion . Your antibodies can attack transfused red blood cells of incompatible types. Mixing certain blood types can have dangerous health consequences. Some types of blood are more common than others, and they vary in compatibility.

This article will discuss how blood types are identified, how rare or common they are, and what that means for you.

Illustration by Lara Antal for Verywell Health

How Many Blood Types Are There?

The ABO system has four major blood types: A, B, AB, and O. Blood types are further categorized by the presence (positive or +) or absence (negative or -) of the Rh(D) antigen on the surface of their red blood cells, also known as the Rh factor . This produces the eight major blood types.

A and B antigens are sugars. The type of sugar antigens a person has determines whether they have A, B, or a mix of A and B (AB). If they lack both A and B, they are type O.

Protein antigens identify if you have a negative or positive Rh factor. A plus (+) or minus (-) sign indicates the presence or absence of the Rh factor. The plus indicates the presence of the antigen, while the minus means it is not widely present. About 85% of the population is Rh positive.

The International Society of Blood Transfusion further divides blood types into blood group systems by other types of antigens that may be present. They have identified 45 different blood group systems with hundreds of different antigens.

Some blood types are found in a limited number of people. In the United States, the blood types each found in less than 5% of the population are:

• AB- : 0.6% of the population
• B- : 1.5% of the population
• AB+ : 3.4% of the population

Most Common

More than 70% of the people in the United States have one of these two common blood types:

• O+ : 37.4% of the population
• A+ : 35.7% of the population

What Is Golden Blood?

Golden blood is the rarest known type of blood in the world. It has no Rh antigens at all, known as Rh null . It is dubbed "golden blood" because it can be donated to people with almost any Rh blood type, including those with rare types of Rh antigens.

However, if people with golden blood need blood, they can only receive the same type of blood. Experts estimate that only about 50 people are known to have golden blood, which was first detected in Australian aboriginal people.

Reasons to Know Your Blood Type

If you need blood during surgery or due to an injury or illness, it's essential to receive blood of a type that is compatible with your own. The hospital laboratory will type your blood and match it to donor units to ensure you only receive compatible blood.

Otherwise, you may have a hemolytic transfusion reaction when your immune system detects foreign proteins on the cells of an incompatible blood type and attempts to destroy them. Transfusion reactions range from mild to life-threatening. They can appear right after a transfusion or up to weeks later.

You can also help others by knowing your blood type in case you are in a position to donate to another individual in need or because blood bank supplies of your type of blood are low.

Different blood types also appear to make people more or less likely to develop certain conditions, including kidney stones, high blood pressure during pregnancy, and bleeding disorders. One study found people with blood group A have a higher likelihood of infection with COVID-19 than those in blood group O.

Compatibility of Different Blood Types

Compatible blood types are based on whether the recipient has antibodies to the donor blood antigens or may develop them.

Early in life, your immune system forms antibodies against A or B antigens  not  present on your red blood cells. People with blood type A will have anti-B antibodies, and those with type B blood will have anti-A antibodies. Type O blood has both anti-A and anti-B antibodies. Type AB blood has neither A nor B antibodies.

Antibodies only form against the Rh factor if an Rh negative person is exposed to Rh positive blood due to transfusion or pregnancy. The following chart shows what types of blood are compatible with each other.

Universal Donors and Recipients

Type O negative blood is called a universal donor , meaning that it can be safely given to people with most other blood types and has a low risk of a transfusion reaction. People with type AB positive blood are known as universal recipients, meaning they can be given almost any type of blood safely.

Unless blood is needed immediately to save a person's life, the hospital laboratory will type the person's blood and perform compatibility testing with the donor blood units (crossmatching) to ensure the safety of the transfusion.

Testing Blood Types in Pregnancy

If you are pregnant, it's important to identify your Rh blood type so you and your healthcare providers can prevent the consequences of Rh incompatibility. This affects only pregnant people who are Rh negative.

If the pregnant person is Rh negative and the other parent is Rh positive, the fetus may be Rh positive. This is called Rh incompatibility.

This incompatibility will not affect a child born during a first incompatible pregnancy. During birth, however, the blood of the pregnant person and fetus mixes. The Rh negative pregnant person can develop antibodies to the Rh factor.

Those antibodies could harm subsequent fetuses that are Rh positive. The pregnant person's anti-Rh(D) antibodies will identify fetal Rh proteins as foreign and attack them. Fetal red blood cells can swell and tear in response, known as hemolytic disease of the fetus and newborn .

This can lower the fetus's or newborn's red blood cell count and lead to serious consequences, such as brain damage, pregnancy loss, or death of the newborn.

An Rh negative pregnant person who has not developed anti-Rh(D) antibodies should given  RhoGAM, or intravenous WinRho, a Rho(D) immune globulin to prevent the development of the antibodies.

How to Find Out Your Blood Type

A blood test can determine your blood type . If you donate blood or plasma , blood typing will be performed at no charge. You can learn your blood type from the report of the donor service.

Blood typing is not a part of routine blood tests. It's commonly ordered if you are having surgery, need a blood transfusion or organ transplant, or are pregnant.

You could request a blood type test from your healthcare provider, but it may not be covered by health insurance if it isn't medically necessary. At a healthcare facility, a small amount of blood will be drawn and sent to a lab for testing.

Check your medical record to see if a blood type test was done in the past and is reported there. If you are unsure how to access your medical record, ask your healthcare provider.

Home blood type tests are available in most states. They are generally accurate if performed correctly. Saliva tests are another option, but they may be more costly and less accurate.

While your blood type doesn't change, a blood type test will be performed each time you need a transfusion. An incompatible transfusion can be fatal, so extreme care is taken to ensure you receive only compatible units.

Blood typing is reported using the ABO blood system and the presence or absence of the Rh(D) antigen known as the Rh factor, resulting in eight major blood types. Some blood types are much more common than others.

If someone needs a blood transfusion, it is essential to use the same or a compatible type of blood to avoid potentially serious reactions to a transfusion. Pregnant people and their healthcare providers must know their Rh factor status to avoid hemolytic disease of the fetus and newborn.

Professional laboratory blood typing is more reliable than home tests, though home blood type tests are available.

Stanford Blood Center. Blood types.

International Society of Blood Transfusion. Red cell immunogenetics and blood group terminology.

Stanford Blood Center. Blood types .

Australian Academy of Science. Rare blood types .

MedlinePlus. Hemolytic transfusion reaction.

Dahlén T, Clements M, Zhao J, Olsson ML, Edgren G. An agnostic study of associations between ABO and RhD blood group and phenome-wide disease risk . Ginsburg D, Wittkopp PJ, Desch KC, eds. eLife. 2021;10:e65658. doi:10.7554/eLife.65658.

Wu SC, Arthur CM, Jan HM, et al. Blood group A enhances SARS-CoV-2 Infection . Blood . 2023;142(8):742-747. doi:10.1182/blood.2022018903

National Library of Medicine. The ABO blood group.

American College of Obstetricians and Gynecologists. The Rh factor: how it can affect your pregnancy.

Myle AK, Al-Khattabi GH.  Hemolytic disease of the newborn: a review of current trends and prospects .  Pediatric Health Med Ther.  2021;12:491-498. doi:10.2147/PHMT.S327032

Eldon Biologicals A/S. Eldoncard: home blood type testing kit .

Velani PR, Shah P, Lakade L.  Determination of ABO blood groups and Rh typing from dry salivary samples.   Int J Clin Pediatr Dent . 2018;11(2):100-104. doi:10.5005/jp-journals-10005-1493

By Nancy LeBrun LeBrun is a Maryland-based freelance writer and award-winning documentary producer with a bachelor's degree in communications.

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Chapter 7 the rh blood group.

The Rh blood group is one of the most complex blood groups known in humans. From its discovery 60 years ago where it was named (in error) after the Rhesus monkey, it has become second in importance only to the ABO blood group in the field of transfusion medicine. It has remained of primary importance in obstetrics, being the main cause of hemolytic disease of the newborn (HDN).

The complexity of the Rh blood group antigens begins with the highly polymorphic genes that encode them. There are two genes, RHD and RHCE, that are closely linked. Numerous genetic rearrangements between them has produced hybrid Rh genes that encode a myriad of distinct Rh antigens. To date, 49 Rh antigens are known.

The significance of the Rh blood group is related to the fact that the Rh antigens are highly immunogenic. In the case of the D antigen, individuals who do not produce the D antigen will produce anti-D if they encounter the D antigen on transfused RBCs (causing a hemolytic transfusion reaction, HTR) or on fetal RBCs (causing HDN). For this reason, the Rh status is routinely determined in blood donors, transfusion recipients, and in mothers-to-be.

Despite the importance of the Rh antigens in blood transfusion and HDN, we can only speculate about the physiological function of the proteins, which may involve transporting ammonium across the RBC membrane and maintaining the integrity of the RBC membrane.

• At a glance

Antigens of the Rh blood group

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Antibodies produced against Rh antigens

• Background information

In 1939, a mother who had just given birth to a still-born child needed a blood transfusion. The ABO blood group system had been discovered almost 40 years previously, and the importance of giving an ABO-compatible blood transfusion was well established. However, although the mother was transfused with ABO compatible blood from her husband, she still experienced an adverse reaction to the transfusion. Her serum was found to contain antibodies that agglutinated her husband's RBCs, even though they were ABO compatible. The death of the mother's fetus and her adverse reaction to a blood transfusion from her husband was related. During the pregnancy, the mother had been exposed to an antigen on the fetal RBCs that was of paternal origin. Her immune system attacked this antigen, and the destruction of the fetal RBCs resulted in fetal death. The mother re-encountered the same paternal antigen when she received a blood transfusion from her husband. This time her immune system attacked the transfused RBCs, causing a hemolytic transfusion reaction. The antibodies responsible led to the discovery of the Rh blood group.

It was wrongly thought that the agglutinating antibodies produced in the mother's serum in response to her husbands RBCs were the same specificity as antibodies produced in various animals' serum in response to RBCs from the Rhesus monkey. In error, the paternal antigen was named the Rhesus factor. By the time it was discovered that the mother's antibodies were produced against a different antigen, the rhesus blood group terminology was being widely used. Therefore, instead of changing the name, it was abbreviated to the Rh blood group.

Remarkably, only 20 years after the discovery of Rh incompatability in pregnancy, effective treatment became available. Today, the Rh status of mothers-to-be is checked during pregnancy to identify those at risk of HDN. In addition, all blood transfusions are matched for the Rh status.

Nomenclature

• Number of Rh antigens: 49
• ISBT symbol: Rh
• ISBT number: 004
• Gene symbols: RHD and RHCE
• Gene names: Rhesus blood group, D antigen; and, Rhesus blood group, CcEe antigens
• Basic biochemistry

Common Rh phenotypes

The most common Rh haplotype in Caucasians, Asians, and Native Americans is DCe. In Blacks, the Dce haplotype is slightly more common ( 1 ).

In Caucasians, the Rh D-negative phenotype results from a deletion of the RHD gene. About 15% of Caucasians are Rh D-negative.

In Africans, there are three molecular backgrounds that give rise to the Rh D-phenotype which is found in 8% of the population. One is the RHD gene deletion that is common in Caucasians. The other two mechanisms are inheriting a RHD pseudogene (contains a duplication of nucleotides that introduces a premature stop codon) or inheriting a RHD hybrid gene (contains nucleotide sequences from the RHCE gene, produces no D antigen and abnormal C antigen) ( 3 )

Uncommon Rh phenotypes

The D antigen contains over 30 epitopes. Variations of the D phenotype arise when these epitopes are only weakly expressed ("weak D phenotype") or when some are missing ("partial D phenotype").

Weak D: all D antigen epitopes are present but are underexpressed

"Weak D" is a Rh phenotype found in less than 1% of Caucasians and is only slightly more common in African Americans ( 2 ). It is typically caused by a single amino acid switch in the transmembrane region of the RhD protein. This disrupts how the RhD protein is inserted into the RBC membrane, reducing the level of expression of RhD. In most cases, adequate levels of D antigen are present and because there has been no change in D epitopes, the formation of anti-D is prevented. Therefore, individuals with the weak D phenotype can receive Rh D-positive blood.

Partial D: some D antigen epitopes are missing

In contrast, people who have been identified as having the "partial D" phenotype should not receive Rh D-positive blood but in practice, people with partial D are difficult to identify. This phenotype is usually caused by the creation of a hybrid RhD and RhCE protein. The hybrid protein is similar enough to RhD to be correctly inserted in the RBC membrane, but it lacks several epitopes found on the complete RhD protein. If a person with the partial D phenotype encounters the complete D antigen on transfused RBCs, they may form anti-D and suffer from a transfusion reaction.

Expression of Rh antigens

The Rh antigens are expressed as part of a protein complex in the RBC membrane. This complex is only expressed in cells of the erythroid line, and therefore Rh antigens are only expressed in RBCs. The composition of the complex is unknown, but it is thought to be a tetramer, consisting of two molecules of Rh-associated glycoprotein (RhAG) and two molecules of Rh proteins. The Rh proteins may be RhD (carrying the D antigen) or RhCE (carrying the C or c antigen and the E or e antigen). It is unknown whether both RhCE and RhD can be in a single complex, but in D-negative individuals the complex would only contain RhCE.

RhAG must be present to direct the Rh antigens to the RBC membrane. If it is missing, none of the Rh antigens are expressed. RHAG is related to the Rh proteins, sharing about 35% of their primary sequence and is the same type of transmembrane protein. However, it is not polymorphic and does not carry Rh antigens itself ( 3 ).

Function of Rh proteins

The Rh antigens are thought to play a role in maintaining the integrity of the RBC membrane—RBCs which lack Rh antigens have an abnormal shape.

Individuals with the rare Rh null phenotype caused by the deletion of RHAG have RBCs that do not express any of the Rh antigens because they cannot be targeted to the RBC membrane. The absence of the Rh complex alters the RBC shape, increases its osmotic fragility, and shortens its lifespan, resulting in a hemolytic anemia that is usually mild in nature. These patients are at risk of adverse transfusion reactions because they may produce antibodies against several of the Rh antigens.

Rh antigens may also be involved in the transport of ammonium across the RBC membrane. Interestingly, the first member of a family of water channels (aquaporins) and the first member of a family of urea transporters were both found in blood group proteins (the Colton blood group and Kidd blood group, respectively).

• Clinical significance of Rh antibodies

The Rh antigens are highly immunogenic, and most of the Rh antibodies should be considered as potential causes of hemolytic transfusion reactions and HDN.

Whereas most blood types are determined by red cell antigens that differ by one or two amino acids, the Rh blood group contains the D antigen which differs from the C/c and E/e antigens by 35 amino acids. This large difference in amino acids is the reason why the Rh antigens are potent at stimulating an immune response ( 4 ).

The majority of antibodies formed against the Rh antigens are of the IgG type. They are capable of causing significant HTR and HDN. Rh antibodies rarely, if ever, bind complement, and therefore RBC destruction is mediated almost exclusively via macrophages in the spleen (extravascular hemolysis).

There are a few examples of Rh alloantibodies that are naturally occurring and are of the IgM type, but they are in the minority.

Transfusion reactions

Anti-D, anti-C, anti-E, and anti-e have all been involved in hemolytic transfusion reactions, particularly delayed reactions ( 5 ).

Routine blood typing for Rh D status in both blood donors and transfusion recipients has reduced the incidence of transfusion reactions caused by anti-D. But sensitization to other Rh antigens can be a problem in transfusion medicine, particularly in patients with sickle cell anemia (SCA). SCA is more common in Blacks, and the treatment of SCA involves blood transfusions. Blacks are also more likely to express variants of the Rh e antigen, and therefore produce anti-e, along with other Rh alloantibodies, which increases the difficulty in finding Rh-compatible blood donors.

Hemolytic disease of the newborn

Anti-D causes the most severe form of HDN and it used to be a major cause of fetal death. Since the introduction of anti-D immunoglobulin along with careful monitoring of at-risk pregnancies, the prevalence of HDN because of Rh D incompatibility has decreased dramatically. However, all cases cannot be prevented, and RhD alloimmunization remains a major cause of disease ( 6 ).

Other Rh alloantibodies that are capable of causing severe HDN include anti-c ( 7, 8 ), which clinically is the most important Rh antigen after the D antigen.

Moderate disease can be caused by anti-C w ( 9 ) and anti-C x ( 10 ). Rh alloantibodies that are typically associated with mild HDN include anti-C (relatively common) ( 11 ), anti-E ( 12 ), and anti-e ( 13 ).

• Molecular information

The Rh locus is located on the short arm of chromosome 1 (on 1p36-p34). It contains the RHD and RHCE genes, which lie in tandem. The RHD and RHCE genes are structural homologs and result from a duplication of a common gene ancestor.

RHD and RHCE each contain 10 exons and span a ~75-kb DNA sequence. The RHD gene is flanked by two 9-kb, highly homologous sequences called "Rhesus boxes" ( 14, 15 ). It is thought that unequal homologous recombination confined to the Rhesus boxes is a common cause of the deletion of the RHD gene, which is found in up to 40% of the population.

View the sequences of RHD and RHCE alleles at the dbRBC Sequence Alignment Viewer

The RHD and RHCE genes each encode a transmembrane protein over 400 residues in length that traverses the RBC membrane 12 times. The RhD protein only differs from the common form of the RhCE protein by about 35 amino acids.

The RhD protein bears the D antigen which has over 30 epitopes. The RhCE protein carries the epitope for the C or c antigen on the second extracellular loop, and the epitope for the E or e antigen on the fourth extracellular loop. A number of nucleotide substitutions in the RHCE gene in turn cause a number of amino acid changes in the RhCE protein, but two polymorphisms are thought to be key in producing the polymorphic antigens on this protein, i.e., the S103P polymorphism (produces the C or c antigen, respectively), and the P226A polymorphism (produces the E or e antigen, respectively).

• 5. Daniels GL. Human Blood Groups. 2nd ed. 2002: Blackwell Science.
• Entrez Gene
• Cite this Page Dean L. Blood Groups and Red Cell Antigens [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2005. Chapter 7, The Rh blood group.
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Ncbi resources.

• The D antigen and CcEe antigens in OMIM
• The RHD locus in Entrez Gene | MapViewer | PubMed Central | PubMed
• The RHCE locus in Entrez Gene | MapViewer | PubMed Central | PubMed
• Alleles of the RHD and RHCE loci in the dbRBC Sequence Alignment Viewer (To view this site, your browser needs to allow pop-ups)

Other Resources

• Read more about the Rh blood group in the Blood Group Antigen Gene Mutation Database

Related information

• OMIM Related OMIM records
• PubMed Links to PubMed
• Gene Locus Links

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