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Blood Typing and Compatibility

Author: Sophia
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what's covered
In this lesson, you will learn about blood typing. You will learn about ABO blood types and the Rh factor, which are both important in matching blood for transfusions. Specifically, this lesson will cover:

Table of Contents

1. Blood Typing

Blood transfusions in humans, in which blood is transferred from one person (a donor) to another (a recipient), were risky procedures until the discovery of the major human blood groups by Karl Landsteiner, an Austrian biologist and physician, in 1900. Until that point, physicians did not understand that death sometimes followed blood transfusions, when the type of donor blood infused into the patient was incompatible with the patient’s own blood. Blood groups are determined by the presence or absence of specific marker molecules (one type of cell surface marker) on the plasma membranes of erythrocytes. These markers are antigens, meaning that the immune system can recognize them and respond to them. With the discovery of erythrocyte antigens, it became possible for the first time to match patient-donor blood types and prevent transfusion reactions and deaths.

You already learned a little bit about antigens. Antigens are substances that may trigger a defensive response from leukocytes of the immune system if the body does not recognize the antigen as belonging to "self." Antigens are generally large proteins but may include other classes of organic molecules, including carbohydrates, lipids, and nucleic acids.

Following an infusion of incompatible blood, erythrocytes with foreign antigens appear in the bloodstream and trigger an immune response. Proteins called antibodies (immunoglobulins), which are produced by certain B lymphocytes called plasma cells, attach to the antigens on the plasma membranes of the infused erythrocytes and cause them to adhere to one another.

  • Because the arms of the Y-shaped antibodies attach randomly to more than one non-self erythrocyte surface, they form clumps of erythrocytes. This process is called agglutination (clumping of blood specifically is called hemagglutination).
  • The clumps of erythrocytes block small blood vessels throughout the body, depriving tissues of oxygen and nutrients.
  • As the erythrocyte clumps are degraded, in a process called hemolysis, their hemoglobin is released into the bloodstream. This hemoglobin travels to the kidneys, which are responsible for the filtration of the blood. However, the load of hemoglobin released can easily overwhelm the kidney’s capacity to clear it, and the patient can quickly develop kidney failure.
More than 50 antigens have been identified on erythrocyte membranes, but the most significant in terms of their potential harm to patients are classified in two groups: the ABO blood group and the Rh blood group.

2. ABO Blood Types

The ABO blood types are genetically determined for every individual based on the presence or absence of specific antigens called “A” or “B” on the individual’s red blood cells. These ABO antigens are glycoproteins.

When an individual has a particular antigen, their immune system is designed to recognize the antigen as self and will not attack it. Unfamiliar antigens are not self, and the immune system will typically recognize these antigens are foreign and stimulate an immune response.

EXAMPLE

An individual with Type A blood has an A antigen on their RBC but has antibodies to the B antigen in their blood.

People whose erythrocytes have A antigens on their erythrocyte membrane surfaces are designated blood type A, and those whose erythrocytes have B antigens are blood type B. People can also have both A and B antigens on their erythrocytes, in which case they are blood type AB. People with neither A nor B antigens are designated blood type O. ABO blood types are genetically determined.

Because of the way that the immune system recognizes and responds to unfamiliar antigens, receiving incompatible blood could lead to a life-threatening reaction. If an individual requires a blood transfusion, it is vital for the donated blood to be compatible with their blood type to avoid this type of reaction.

The table below shows the different blood types and associated antigens and antibodies, as well as their compatible blood types. This figure focuses only on ABO blood types; note that other factors must be considered in selecting blood for a transfusion. Note that type A blood has a specific antigen on the surface of the erythrocytes, while type B blood has a different antigen on the surface of its erythrocytes. Type AB blood has both of these antigens, type A and type B, while type O has neither of these antigens. In the plasma, type A blood has anti-B antibodies, type B blood has anti-A antibodies, type AB blood has neither type A nor type B antibodies, and type O blood has both type A and type B antibodies. This allows the body to recognize blood of a different type, leading to a reaction. If antibodies are present to an antigen on blood cells, a reaction occurs. Therefore, an individual with type A blood can only receive A or O blood; an individual with type B blood can only receive B or O blood; an individual with type AB blood is a universal recipient that can accept any of these blood types, and an individual with type O blood can only receive type O blood but is a universal donor.

Blood Type

A B AB O
Red Blood Cell Type Red Blood Cell Type A is shown. Type A has a different antigen to type B. Red Blood Cell Type B is shown. Red Blood Cell type AB is shown. Type AB has both antigens. Red Blood Cell type O is shown. Type O has neither antigen.
Antibodies in Plasma Type A blood contains type B antibodies.
Anti-B 		Type B blood contains type A antibodies.
Anti-A 		None Type AB blood has neither A nor B antibodies, and type O blood has both A and B antibodies.
Anti-A and Anti-B
Antigens in Red Blood Cell Each antigen has a different structure. None
Blood Types Compatible in an Emergency A, O B, O A, B, AB, O
(AB⁺ is the universal recipient) 		O
(O is the universal donor)

The animation below shows what happens when blood of the same or different types is combined. Note which combinations cause coagulation as antibodies bind to antigens on blood cells.

Four labeled red blood droplets are shown in a row across the screen, each with a round shape superimposed over part of the top part of the droplet containing a red blood cell with specific antigens protruding around the border of the red blood cell. The first droplet has the letter A superimposed on it, and the red blood cell has antigens that are purple. This droplet is labeled above as ‘Type A’. The second droplet has the letter B superimposed on it, and the red blood cell has antigens that are blue. This droplet is labeled above as ‘Type B’. The third droplet has the letters AB superimposed on it and the red blood cell has both purple and blue antigens. This droplet is labeled above as ‘Type AB’. The 4th droplet has the letter O superimposed on it and it has black antigens. This droplet is labeled above as ‘Type O’. Everything on screen fades out, and two identical droplets labeled as Type A appear side by side in the center of the screen. They move toward each other and smoothly merge to form one droplet. A white check mark appears inside a small green circle at the lower right corner of the droplets merging. Above this appears the text ‘Type A + Type A = Compatible’. This fades out and a type A droplet appears side by side to a type B droplet, both in the center of the screen. Both the type A and the type B droplet have a round shape superimposed over part of the top part of the droplet containing a red blood cell with specific antigens protruding around the border of the red blood cell. The antigens of the type A droplet are purple, and the antigens of the type B droplet are blue. The type A droplet merges with the type B droplet and teal Y-shaped antibodies appear, binding to antigens as red blood cells clump together significantly. A red ‘X’ appears in the bottom right corner of the frame of the droplets. Text appears at the top of the screen that reads ‘Type A + Type B = Hemagglutination’. This text and all images fade out, and text appears at the top of the screen that reads ‘Type O = Universal Donor’. Three droplets in a row are shown under this text; one labeled type A, one labeled type B, and one labeled type AB. A droplet labeled type O is shown below the three droplets in its own row. The type O droplet smoothly merges with the type A droplet, type B droplet, and type AB droplet successively with a black arrow pointing toward each respective merge, as a white checkmark in a green circle appears with each merge. This text and all images fade out, and text appears at the top of the screen that reads ‘Type AB = Universal Recipient’. Three droplets in a row are shown under this text; one labeled type A, one labeled type B, and one labeled type O. A droplet labeled type AB is shown below the three droplets in its own row. The type AB droplet smoothly merges with the type A droplet, type B droplet, and type O droplet successively with a black arrow pointing toward each respective merge, as a white checkmark in a green circle appears with each merge. This text and all images fade out, and a type O negative droplet is shown at the left center of the screen, labeled ‘Type O-’. A few green Y-shaped antibodies appear around the droplet as red blood cells also appear that clump together significantly. A white X in a red circle appears to the right left corner of the droplet. A type AB positive droplet is shown at the right center of the screen, labeled ‘Type AB+’. A few yellow Y-shaped antibodies appear around the droplet as red blood cells also appear that clump together significantly. A white X in a red circle appears to the right left corner of the droplet. At the top of the screen appears text that reads ‘Remember that other antigens also affect compatibility’.

try it
If an individual with type AB blood is given a transfusion of type A blood and all non-ABO blood group antigens are compatible, will hemagglutination occur?
No, hemagglutination will not occur. An individual with type AB blood has the A antigen on their red blood cells, and the other antigens are compatible, so no reaction will occur.
If an individual with type A blood is given a transfusion of type O blood and all non-ABO blood group antigens are compatible, will hemagglutination occur?
No, hemagglutination will not occur. Type O blood does not have A or B antigens on its surface, and all other antigens are compatible, so no reaction will occur.

3. Rh Factor

In addition to the A, B, AB, or O blood type, individuals may have another antigen on their red blood cells called Rh factor.

The Rh blood group is classified according to the presence or absence of this second erythrocyte antigen, identified as Rh. (It was first discovered in a type of primate known as a rhesus macaque, which is often used in research, because its blood is similar to that of humans.) Although dozens of Rh antigens have been identified, only one, designated D, is clinically important. Those who have the Rh D antigen present on their erythrocytes—about 85 percent of Americans—are described as Rh positive (Rh⁺), and those who lack it are Rh negative (Rh⁻).

Note that the Rh group is distinct from the ABO group, so any individual, no matter their ABO blood type, may have or lack this Rh antigen. When identifying a patient’s blood type, the Rh group is designated by adding the word positive or negative to the ABO type. Individuals who have the antigen on their RBCs are described as Rh positive (Rh⁺), and those who lack the antigen are described as Rh negative (Rh⁻).

When identifying a patient’s blood type, the Rh factor is designated by adding the word positive or negative to the ABO type.

EXAMPLE

A positive (A⁺) means A blood type with the Rh antigen present, and AB negative (AB⁻) means AB blood type without the Rh antigen.

Individuals receiving blood transfusions must receive donated blood that matches their Rh type, or a serious, life-threatening reaction will occur.

During pregnancy, the fetus can be significantly affected if the mother has a different Rh factor. If an Rh⁻ mother conceives a Rh⁺ baby, her Rh antibodies can cross the placenta and destroy the fetal RBCs. This condition is known as hemolytic disease of the newborn and can be so severe that, without treatment, the fetus may die in the womb or shortly after birth. A medication known as RhoGAM can temporarily prevent the development of Rh antibodies in an Rh- mother, thereby averting this potentially serious disease for the fetus if it is Rh⁺. RhoGAM is administered to Rh- mothers during weeks 26−28 of pregnancy and within 72 hours following birth.

Note that you may sometimes see the term Rh D antigen. There are actually several types of Rh antigens, but Rh D is the one you will hear about regularly with respect to blood donation. The presence or absence of the Rh D antigen is what determines if your blood type is Rh positive or Rh negative, although other Rh antigens are also considered for compatibility as needed. The reason is that the Rh D antigen produces the strongest immune response (NHS, n.d.).

summary
In this lesson, you learned about blood typing. Specifically, you learned about ABO blood typing and the Rh factor, which determines Rh blood type. This information is important in understanding how compatibility for blood transfusions is determined and why it is essential to use well-matched blood for blood transfusions.

SOURCE: THIS TUTORIAL HAS BEEN ADAPTED FROM (1) “OPEN RN | MEDICAL TERMINOLOGY – 2E” BY ERNSTMEYER & CHRISTMAN AT OPEN RESOURCES FOR NURSING (OPEN RN). (2) "MEDICAL TERMINOLOGY" BY HOBBS & CASTEEL AT PHOENIX COLLEGE NURSING. ACCESS FOR FREE AT WTCS.PRESSBOOKS.PUB/MEDTERM/ AND OPEN.MARICOPA.EDU/MEDICALTERMINOLOGY/FRONT-MATTER/INTRODUCTION/. LICENSING: CREATIVE COMMONS ATTRIBUTION 4.0 INTERNATIONAL.

REFERENCES

The Rh System. (n.d.). NHS Blood and Transplant. The RH system - NHS Blood Donation

Terms to Know
ABO Antigen

One of the antigens that produce the ABO blood types; these are glycoproteins.

Agglutination

Something clumping (such as red blood cells clumping together).

Antigen

A substance that can be recognized by the immune system (for example, a component of a microbe or on the surface of a red blood cell).

Blood Transfusion

A procedure in which blood is transferred from one person (a donor) to another (a recipient).

Cell Surface Marker

Substances on the surfaces of cells, such as the ABO antigens, that are involved in cell-cell interactions and recognition, among other functions.

Erythrocyte Antigen

A substance on the surface of a red blood cell that can be recognized by the immune system.

Hemagglutination

Clumping of red blood cells.

Hemolytic Disease of the Newborn

A condition in which an Rh⁻ mother conceives an Rh⁺ baby and antibodies to the Rh factor cross the placenta, causing severe complications and potentially death of the baby if not treated.

Rh D Antigen

The Rh antigen that produces the strongest immune response and that is most important in blood typing.

Rh Factor

An antigen found on human red blood cells.

Rh Negative (Rh⁻)

Red blood cells that lack the Rh factor (an antigen).

Rh Positive (Rh⁺)

Red blood cells that have the Rh factor (an antigen).

Rh blood group

The blood group determined by the presence or absence of the Rh antigens (whether an individual is Rh positive or negative is determined only by the Rh D antigen).

RhoGAM

A medication that can prevent the development of Rh antibodies in an Rh⁻ mother carrying an Rh⁺ fetus, preventing hemolytic disease of the newborn

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