Blood type

Blood group redirects here.

A total of 29 human blood group systems are recognized by the International Society of Blood Transfusion (ISBT). Each blood group is represented by a substance on the surface of red blood cells (RBCs). These substances are important because they contain specific sequences of amino acid and carbohydrate which are antigenic. A complete blood type describes the set of 29 substances on the surface of RBCs and other tissues, and an individual's blood type is one of the many possible combinations of blood group antigens, but usually only the two main blood group systems, ABO and Rhesus, are determined and used to describe the blood type. Over 400 different blood group antigens have been found, many of these being very rare. If an individual is exposed to a blood group antigen that is not recognised as self, the individual can become sensitized to that antigen; the immune system makes specific antibodies which binds specifically to a particular blood group antigen and an immunological memory against that particular antigen is formed. These antibodies can bind to antigens on the surface of transfused red blood cells (or other tissue cells) often leading to destruction of the cells by recruitment of other components of the immune system. Knowledge of a individual's blood type allows identification of appropriate blood for transfusion.

Several different antigens stemming from one allele (or very closely linked gene) are collectively labeled as a blood group system (or blood group). The two most important blood group systems were discovered during early experiments with blood transfusion, the ABO group in 1901 and the Rhesus group in 1937 . These two blood groups are reflected in the common nomenclature A positive, O negative, etc. with letters referring to ABO group and positive/negative to the presence of the RhD antigen of the Rhesus group. Development of the Coombs test in 1945 and the advent of transfusion medicine led to discovery of the remainder of the blood groups. The Coombs test is important in the screening of blood for blood group antibodies in the preparation of blood for transfusion.

Blood types are inherited and represent contributions from both parents. Some blood types are rare, and are primarily found in certain ethnic groups. Some blood types are associated with inheritance of other diseases, such the Kell antigen is associated with McLeod syndrome. Some blood types help protect from disease, such as the Duffy antigen giving partial resistance to malaria. Rarely, a person's blood type changes through addition or suppression of an antigen in infection or malignancy.

Serious reactions can occur if a person is exposed to blood of a different blood type. In blood transfusion, mismatches involving minor antigens or weak antibodies may lead to minor problems; however, more serious incompatabilities can lead to a more vigorous immune response with massive RBC destruction, low blood pressure, and even death.

Often, pregnant women carry a fetus with a different blood type to herself, and sometimes the mother will form antibodies against the red blood cells of the fetus, leading to low fetal blood counts, a condition known as hemolytic disease of the newborn.

Introduction

ABO and Rhesus: the two main blood group systems

The ABO system is the most important blood type system in human blood transfusion. The associated anti-A antibodies and anti-B antibodies are usually powerful IgM antibodies. ABO IgM antibodies are produced in the first years of life by sensitization to environmental substances such as food, bacteria and viruses.

The Rhesus system is the second most important blood type system in human blood transfusion. The most important Rhesus antigen is the RhD antigen because it is the most immunogenic of the five main rhesus antigens; however, anti-RhD antibodies are not usually stimulated by environmental substances. Powerful IgG antibodies can be produced when RhD positive RBCs are transfused into a RhD negative individual.

**Distribution of ABO and Rh Blood types (averages for each population)**
Population	O+	A+	B+	AB+	O−	A−	B−	AB−
USA	38%	34%	9%	3%	7%	6%	2%	1%
UK	37%	35%	8%	3%	7%	7%	2%	1%
Australia	40%	31%	8%	2%	9%	7%	2%	1%
Finland	27%	38%	15%	7%	4%	6%	2%	1%
Sweden	32%	37%	10%	5%	6%	7%	2%	1%

Other human blood group systems

The International Society of Blood Transfusion currently recognizes 29 blood group systems (including the ABO and Rh systems). Thus, in addition to the ABO antigens and Rhesus antigens, many other antigens are expressed in the RBC surface membrane. For example, an individual can be AB RhD positive, and at the same time M and N positive (MNS system), K positive (Kell system), Le^a or Le^b positive (Lewis system), and so on for each blood group system. Many of the blood group systems were named after the patients in whom the corresponding antibodies were initially encountered.

Importance for transfusions

Transfusion medicine is a specialized branch of hematology that is concerned with the study of blood group antigens and blood group antibodies, along with the work of a blood bank to provide a transfusion service for blood and other blood products. Across the world blood products must be prescribed by a medical doctor (licensed physician or surgeon) in a similar way to medicines. In the USA blood products are tightly regulated by the Food and Drug Administration.

Blood transfusions between donor and recipient of incompatible blood types can cause severe acute immunological reactions, hemolysis (RBC destruction), renal failure, shock, and sometimes death. Antibodies can be highly active and can attack RBCs and bind components of the complement system to cause massive hemolysis of the transfused blood.

Hemolytic disease of the newborn

An antenatal woman can make IgG blood group antibodies, if her fetus has a blood group antigen that she does not. This can happen if some of the fetuses blood cells pass into the mother's blood circulation (ie a small fetomaternal hemorrhage at the time of child birth) or sometimes after a therapeutic blood transfusion. This can lead to Rh disease or another forms of hemolytic disease of the newborn (HDN) in her current baby or in subsequent pregnancies. Some blood groups can cause severe HDN, some can only cause mild HDN and others are not known to cause HDN.

Compatibility

Blood products

In order to provide maximum benefit from each blood donation and to extend shelf-life, blood banks fractionate whole blood into several products. The most common of these products are packed RBCs, plasma, platelets, cryoprecipitate, and fresh frozen plasma (FFP). FFP is quick-frozen to retain labile clotting factors V and VIII and usually administered to patients who have a potentially fatal clotting problem caused by a condition such as advanced liver disease, overdose of anticoagulant, or disseminated intravascular coagulation (DIC).

Cross matching blood

A patient should ideally receive their own blood or type-specific blood products to minimize the chance of a transfusion reaction. If time allows, the risk will further be reduced by cross-matching blood, in addition to blood typing both recipient and donor. Cross-matching involves mixing a sample of the recipient's blood with a sample of the donor's blood and checking to see if the mixture agglutinates, or forms clumps. Blood bank technicians usually check for agglutination with a microscope, and if it occurs, that particular donor's blood cannot be transfused to that particular recipient. Blood transfusion is a potentially risky medical procedure, so cross-matching is standardized using a barcode system known as ISBT 128.

RBC compatibility

Blood group A individuals have red blood cells with the A antigen on their surface, and blood serum containing antibodies against the B antigen. Therefore, a group A person can only receive blood from people in groups A or O (with A being preferable).
Blood group B individuals have red blood cells with the B antigen on their surface, and blood serum containing antibodies against the A antigen. Therefore, a group B person can only receive blood from people in groups B or O (preferably B).
Blood group AB individuals have red blood cells with both A and B surface antigens, and their blood serum does not contain antibodies against either A or B antigen. Therefore, a person with type AB blood can receive blood from any group (preferably AB) but cannot donate blood except to another AB.
Blood group O individuals have red blood cells with neither A or B surface antigen, but their blood serum contains antibodies against both A and B antigens. Therefore, a group O person can only receive blood from group O.

**RBC compatibility table**
Recipient blood type	Donor must be
AB+	Any blood type
AB-	O-	A-	B-	AB-
A+	O-	O+	A-	A+
A-	O-	A-
B+	O-	O+	B-	B+
B-	O-	B-
O+	O-	O+
O-	O-

An RhD negative patient (who has not been sensitized to RhD positive RBCs and who does not have any anti-D antibodies) can receive RhD positive blood cells, but there is a high probability that this would sensitize the patient to the RhD antigen, and a female patient would risk HDN. Therefore RhD positive blood is never given to RhD negative women of childbearing age, and is only given to other RhD negative patients in extreme circumstances, such as a major bleed when RhD negative red cells are running short. If a RhD negative patient has developed anti-D antibodies, a second exposure to RhD positive blood would lead to a potentially dangerous transfusion reaction. Occasionally, for transfusion of males or women above child-bearing age, RhD positive blood is given to a RhD negative individual (who do not have atypical red cell antibodies) when it is necessary to conserve RhD negative blood stocks in the blood bank for use in people where sensitisation to RhD antigens could cause serious problems. The converse is not true: RhD positive patients do not react to RhD negative blood.

Plasma compatibility

Donor-recipient compatibility for blood plasma is the reverse from that of RBCs. Plasma extracted from type AB blood can be transfused to individuals of any blood group, but type O plasma can only be used by type O recipients.

Rhesus D antibodies are not usually naturally occuring, so generally both RhD negative and RhD positive blood do not contain anti-RhD antibodies, and so generally RhD negative or RhD positive donor blood plasma can be transfused into both RhD negative and RhD positive recipients. Hence, there is no need to specify RhD positive or RhD negative in the table below. If anti-RhD antibodies have developed in a donor these would be detected by antibody screening in the blood bank. Donor blood containing anti-RhD antibodies would not be suitable for transfusion into a RhD positive patient, but anyone with any strong atypical blood group antibodies would not be accepted as a blood donor.

**Plasma compatibility table**
Recipient blood type	Donor must be
AB	AB
A	A or AB
B	B or AB
O	Any blood type

Universal donors and universal recipients

Individuals with blood type O negative are often called universal donors and individuals with type AB positive blood are called universal recipients, but the terms universal donor and universal recipient are not very useful, because they only consider the reaction of the patient's antibodies to received red blood cells, and not the antibodies present in the transfused blood. These terms may be generally true for transfusions of packed red cells, where as much of the plasma as possible has been removed. Thus, although a transfusion of O negative blood to a patient of blood group A or B is unlikely to produce an immune reaction due to the recipient's antibodies, the transfused blood may itself contain antibodies to the patient's A and B antigens; this can cause an adverse reaction, although the risk is far less than that of an O negative patient receiving types A or B. For this reason an exact ABO-type match is preferable where circumstances allow. Additionally, the other red blood cell surface antigens that belong to blood groups outside of the ABO blood group system might cause an adverse reaction if they can bind the corresponding antibodies.

With respect to transfusions of plasma this situation is reversed. Type O plasma can only be given to O recipients, while AB plasma (which does not contain anti-A or anti-B antibodies) can be given to patients of any ABO blood group.

Transfusion are further complicated because platelets and WBCs have their own systems of surface antigens and sensitization to platelet or WBC antigens can occur as a complication of transfusion.

Miscellaneous

Blood types have applications in forensic science and in paternity testing; however, they are being replaced by DNA studies which provide greater certitude.

For RhD negative people, there is a risk associated with travelling to parts of the world where supplies of RhD negative blood are rare, particularly East Asia. Correspondingly, blood services in these areas may look to encourage westerners to donate blood.

Some blood types may offer protection from certain disorders and illnesses. For example, Duffy blood group is related to immunity against some kinds of malaria, and is more common in ethnic groups from areas with a high incidence of malaria, probably as a result of natural selection.

The Japanese blood type theory of personality is a popular belief that a person's ABO blood type is predictive of their personality, character, and compatibility with others. This belief has carried over to certain extent in other parts of East Asia such as South Korea and Taiwan. In Japan, asking someone their blood type is considered as normal as asking their astrological sign. It is also common for Japanese-made video games (especially Role-Playing Games) to include blood type with character descriptions.

Some front-line military personnel choose to be tattooed with their blood type in case they should need an emergency blood transfusion.

Rare blood types can cause supply problems for blood banks and hospitals. For example, U-negative and Duffy-negative are two blood groups that occur only within people of African origin, and even then they are rare traits. The rarity of these factors can result in a shortage of U-negative and Duffy-negative blood for patients of African ethnicity.

The ABO antigen is also expressed on the von Willebrand factor (vWF) glycoprotein, which participates in hemostasis (control of bleeding). In fact, having type O blood predisposes very slightly to bleeding, as vWF is degraded more rapidly.

In Nazi Germany research was done to associate B-type blood type with inferior personal characteristics. B-type blood was relatively common among German Jewish populations. This research has since been discredited.

The blood type diet is a system whereby people modify their food intake and lifestyle according to their ABO blood group and secretor status for health.

References

Mollison PL, Engelfriet CP and Contreras M. Blood Transfusion in Clinical Medicine. 1997. 10th edition. Blackwell Science, Oxford, UK.

External links

(ABO) and (Rh/D)
ABO World Japanese Blood Typing theory (web site in Japanese)
All about blood groups bloodbook.com
Alternative Definition of blood group
Asian Blood ABO allele distribution among Asians
Australian blood statistics - Aust. Red Cross Blood Service
Blood type diet - dadamo.com
Definition of Blood Group - Merriam-Webster
History of ABO blood types Blood group serology--the first four decades (1900--1939).
Racial & Ethnic Distribution of ABO Blood Types - bloodbook.com
Racial and Ethnic distribution of Rh blood types - madsci.org
Rare blood groups - LifeShare blood center

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