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:

1. Type A: Has A antigens on the red cells and anti-B antibodies in the plasma.
2. Type B: Has B antigens with anti-A antibodies in the plasma.
3. Type AB: Has both A and B antigens, but no anti-A or anti-B antibodies. Known as the universal recipient.
4. 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:

1. A+
2. A-
3. B+
4. B-
5. AB+
6. AB-
7. O+
8. O-

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.

• Note: “Yes” indicates compatibility for a transfusion between the donor and recipient blood types.

1. Type 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).
2. 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.
3. 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.
4. 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:

1. MNS System: This system depends on the presence or absence of M, N, S, s, and U antigens.
2. 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-).
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. 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:

1. 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.
2. 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.

1. 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.
2. 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.
3. 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.

References

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• 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