Blood groups and blood transfusions

Question 1

What is an antigen?

Answer 1

An antigen is a substance that can stimulate an immune response, such as the formation of antibodies.

Question 2

What is an antibody?

Answer 2

An antibody is a protein that is produced by the body in response to the introduction of a foreign antigen.

Question 3

Are antigen-antibody reactions specific?

Answer 3

Yes, antigen-antibody reactions are specific, meaning that a given antibody will react only with its corresponding antigen.

Question 4

What are blood groups?

Answer 4

Blood groups are systems of antigens in which the antigen specificity is controlled by specific genes. An example is the ABO blood group system.

Question 5

What does “agglutinate” mean?

Answer 5

“Agglutinate” means to clump.

Question 6

What is an agglutinin?

Answer 6

An agglutinin is something that causes clumping, such as IgM antibodies.

Question 7

What is a monoclonal antibody?

Answer 7

A monoclonal antibody is a laboratory-produced and cloned molecule that binds specifically to one epitope, which is the bit of the antigen that an antibody recognizes.

Question 8

What is the important concept in transfusion related to producing antibodies?

Answer 8

The concept is that you can only produce antibodies to antigens that you do not have.

Question 9

What are blood group antigens?

Answer 9

Blood group antigens are molecules that are present on the surface of red blood cells, platelets, and other body tissues.

Question 10

How are blood group antigens inherited?

Answer 10

Blood group antigens are inherited characteristics, with blood group genes either coding for red cell membrane proteins directly or for enzymes that cause the production of specific red cell membrane carbohydrate sugars via mRNA.

Question 11

Why are blood group systems important?

Answer 11

Blood group systems are important because we can make antibodies to antigens that we do not have when we are exposed to such antigens. This can happen after a blood transfusion when exposed to antigens you lack or during pregnancy where fetal RBCs expressing antigens the mother doesn’t have (i.e., from dad) cross into maternal circulation.

Question 12

What can lead to the formation of blood group antibodies?

Answer 12

Sensitizing events can lead to the formation of blood group antibodies.

Question 13

What are the potential consequences of blood group antibodies?

Answer 13

The consequences of blood group antibodies can include immediate catastrophic intravascular hemolysis via complement activation in the case of ABO incompatibility, delayed hemolytic transfusion reactions, hemolytic disease of the fetus and newborn (HDFN), and problems in selecting blood for regularly transfused patients.

Question 14

What is the significance of the ABO system in transfusion?

Answer 14

The ABO antigens are the most important blood group in relation to transfusion, and they are also expressed on most endothelial and epithelial membranes, with implications for ABOi solid organ and bone marrow transplantation. There are four main groups: A, B, AB, O, with racial variation in population frequency.

Question 15

What is the structure of the terminal sugars in the ABO blood antigens?

Answer 15

Red blood cell glycoproteins or glycolipids have a terminal sugar fucose (H substance), and one of two enzymes (shown in pink) can add another sugar, either galactose or N-acetylgalactosamine, to the antigen, making B antigen or A antigen, respectively.

Question 16

What is the autosomal co-dominance of A and B alleles in blood groups?

Answer 16

Blood groups exhibit autosomal co-dominance of A and B alleles, where the phenotype and antigens depend on the genotype and presence of these alleles.

Question 17

How can you establish a patient’s blood group based on antigen-forward grouping?

Answer 17

A sample of the patient’s RBCs (i.e., antigen) is used and reacted against test monoclonal anti-A and anti-B grouping anti-sera. IgM antibodies cause hemagglutination of the red blood cells, which appears as ‘clumping’ and formation of an aggregate where antigen and antibody react.

Question 18

What are the universal donor and universal recipient blood groups for RBCs?

Answer 18

Blood group O- is the universal donor as there are no antigens to react with antibodies in patients’ blood, and blood group AB- is the universal recipient as there are no antibodies in patients’ blood to ABO antigens, so they can receive blood from any group.

Question 19

Why do we develop ABO antibodies?

Answer 19

In the absence of corresponding antigens, ABO antibodies form during the first few months after birth. For example, a blood group A baby will start to make anti-B antibodies, probably as a result of exposure to ABH antigen-like substances in the diet or environment. These antibodies are mainly IgM, but they can also be IgG.

Question 20

How can you confirm a patient’s blood phenotype indirectly using reverse grouping?

Answer 20

Methods can be employed to detect the antibodies in a patient’s serum to confirm the blood phenotype, essentially as a ‘double checking’ mechanism that is the opposite of forward grouping.

Question 21

What are the potential consequences of acute hemolytic transfusion reactions due to ABO incompatibility?

Answer 21

Acute hemolytic transfusion reactions due to ABO incompatibility can cause red blood cell destruction and intravascular hemolysis, which can lead to cardiovascular collapse, shock, renal failure, and DIC (disseminated intravascular coagulation). About 1/180,000 red cell units transfused may be ABOi, and major morbidity occurs in 30% of cases, with 5-10% of episodes contributing to the death of the patient.

Question 22

What is the Rh blood group system?

Answer 22

The Rh blood group system is a group of antigens that are a component of red blood cell transmembrane proteins. Two genes, RhD and RhCE, are responsible for the antigens, with the RhD encoding for the membrane protein with the D antigen, and the RhCE encoding for membrane proteins with c or C and e or E antigens (eight possible gene or haplotype combinations).

Question 23

How do you check for the D antigen in the Rh blood group system?

Answer 23

You either have the D antigen or not, meaning you are either RhD+ or RhD-. The D antigen is a dominant trait, with approximately 85% of the European population being Rh+. This means that approximately 15% of the population are Rh- and therefore can make antibodies to D antigen if exposed to it via transfusion or pregnancy. There is variation in different ethnicities, with some groups having an intact gene that is not expressed or only expressed at very low levels, such as Japanese and Black Africans.

Question 24

Why is the D antigen the most clinically significant of the Rh antigens?

Answer 24

The D antigen is the next most important antigen after ABO antigens and is the most clinically significant of the Rh antigens.

Question 25

What is the nature of the D antigen in terms of its antigenicity and immunogenicity?

Answer 25

The D antigen is very antigenic, giving strong reactions with antibody, and very immunogenic, meaning that it is very good at stimulating the production of anti-D antibody in D-negative people who are exposed to D antigen.

Question 26

What type of antibodies are produced in response to the D antigen?

Answer 26

Antibodies produced in response to the D antigen are predominantly IgG.

Question 27

What is sensitization in the context of the Rh blood group system?

Answer 27

Sensitization refers to the stimulation of the production of anti-D antibody after exposure to D antigen.

Question 28

What is the potential consequence of sensitization to the D antigen in pregnancy?

Answer 28

Sensitization to the D antigen during pregnancy can result in the development of hemolytic disease of the fetus and newborn, which can cause anemia, jaundice, and other complications. To prevent this, Rh-negative women who have been exposed to Rh-positive blood are given anti-D immunoglobulin to prevent sensitization.

Question 29

How can sensitization to the D antigen be prevented in pregnancy?

Answer 29

Sensitization to the D antigen can be prevented in pregnancy through a number of measures. These include booking maternal blood samples for ABO and Rh group and red cell alloantibody screen at 10-12 weeks gestation, routine antenatal anti-D prophylaxis (RAADP) for RhD- non-sensitized women, administration of anti-D IgG to a Rh- mother to protect against sensitization from a Rh+ fetus, and further doses of anti-D immunoglobulin after 'sensitizing' events to 'mop up' D antigen that has come over the placenta from mother to baby, such as delivery, miscarriage, CVS, amnio, fall, trauma, or APH.

Question 30

What is the Kleihauer test, and how is it used in pregnancy?

Answer 30

The Kleihauer test is a blood test that is used to estimate the volume of fetal red blood cells in maternal circulation. The test looks for fetal cells and estimates their volume, with red cells indicating fetal red blood cells and pale cells indicating maternal red blood cells.

Question 31

What is flow cytometry, and how is it used in pregnancy?

Answer 31

Flow cytometry is a laboratory technique that is used to analyze the properties of cells and particles in a fluid. In pregnancy, it is used to confirm the volume of fetal red blood cells in maternal circulation and give further anti-D if needed.

Question 32

What are the minimum compatibility requirements for transfusion for all patients?

Answer 32

he minimum compatibility requirements for transfusion for all patients include ABO compatibility, Rh D negative for Rh D negative patients, and Kell negative for Kell negative patients. Women of childbearing potential are also screened for Rh D status.

Question 33

What is extended match transfusion, and when is it used?

Answer 33

Extended match transfusion involves matching patients for the full Rh system and Kell antigens, in addition to the minimum compatibility requirements. This is typically used for frequently transfused patients.

Question 34

What blood components are typically used for transfusion?

Answer 34

Whole blood is rarely used for transfusion, and blood component therapy is typically used instead. The blood components used for transfusion include red blood cells (RBCs), fresh frozen plasma (FFP), platelets, cryoprecipitate, and buffy coats.

Question 35

What are plasma derivatives, and what products are included in this category?

Answer 35

Plasma derivatives are licensed medicinal products that are manufactured from human plasma donations. Products included in this category include human albumin solution (HAS), clotting factor concentrates, and immunoglobulin solutions.

Question 36

What is the donor eligibility questionnaire used for in transfusion medicine?

Answer 36

The donor eligibility questionnaire is used to assess the health, lifestyle, travel history, medical history, and medications of potential blood donors to determine their suitability for donation.

Question 37

What is done to minimize the transmission of prion-associated diseases during transfusion?

Answer 37

Specific precautions are taken to reduce the transmission of prion-associated diseases, including variant Creutzfeldt-Jakob disease (vCJD), during transfusion. These precautions may include screening of donors and/or the use of prion-reduction technologies.

Question 38

What types of screening are routinely performed on donated blood?

Answer 38

Routinely, donated blood is screened for hepatitis B, HIV 1 and 2, hepatitis C, HTLV I and II, and syphilis.

Question 39

: What special circumstances may require additional screening of donated blood?

Answer 39

Special circumstances that may require additional screening of donated blood include malarial antibodies, West Nile virus antibodies, and Trypanosoma cruzi antibodies.

Question 40

What are some special requirements for blood products used in transfusion?

Answer 40

Some special requirements for blood products used in transfusion include irradiation, washing of red cells/platelets, use of single-donor platelets rather than a pool, HLA/HPA selection, pathogen-inactivated fresh frozen plasma, and CMV-negative products.

Question 41

What is the transfusion process, and what are some key steps involved?

Answer 41

The transfusion process begins with the identification of a need for transfusion, followed by prescription of the appropriate blood product. The patient is cannulated and blood is sent for cross-matching, with two samples required at different times. The laboratory then finds suitable units, which are transported to the clinical area. Prior to transfusion, a nurse checks the patient and the product, and monitoring begins once transfusion is initiated.