Blood Groups Introduction
- Blood groups are determined by the presence of antigen in RBC membrane. When blood from two individuals is mixed, sometimes clumping (agglutination) of RBCs occurs.
- This clumping is because of the immunological reactions. But, why clumping occurs in some cases and not in other cases remained a mystery until the discovery of blood groups by the Austrian Scientist Karl Landsteiner in 1901. He was honored with Nobel Prize in 1930 for this discovery.
ABO Blood Groups
- The determination of ABO blood groups depends upon the immunoloc|ical reaction between antigen and antibody.
- Landsteiner found two antigens on the surface of RBCs and named them as A antigen and B antigen. These antigens are also called agglutinogens’ because of their capacity to cause agglutination’ of RBCS.
Read And Learn More: Medical Physiology Notes
Table of Contents
- He noticed the corresponding antibodies or agglutinins in the plasma and named them anti-A or α antibody and anti-B or β antibody.
- However, a particular agglutinogen and the corresponding agglutinin cannot be present together. If present, it causes clumping of the blood.
- Based on this, Landsteiner classified the blood groups. Later it has become the “Landsteiner’s Law” for grouping the blood.
Landsteiner’S Law: Landsteiner’s law states that
- If a particular antigen (agglutinogen) is present in the RBCs, the corresponding antibody (agglutinin) must be absent in the serum.
- If a particular antigen is absent in the RBCs, the corresponding antibody must be present in the serum. Though the second part of Landsteiner’s law is a fact, it is not applicable to Rh factor.
Blood Group Systems: More than 20 genetically determined blood group systems are known today. But, Landsteiner discovered two blood group systems called the ABO system and Rh system. These two blood group systems are the most important ones that are determined before blood transfusions.
ABO Systems: Based on the presence or absence of antigen A and antigen B, blood is divided into four groups
- ‘A’ group
- ‘B’ group
- ‘AB’ group
- ‘O’ group.
- The blood having antigen A is called A group. This group has β antibody in the serum. The’blood with antigen B and α antibody is called the B group.
- If both the antigens are present; the blood group is called AB group and serum of this group does not contain any antibody. If both antigens are absent, the blood group is called O group and both β and α antibodies are present in the serum.
- The antigens and antibodies present in different groups of ABO system are given in Table. Percentage of, people among Asian and European populations belonging to different blood group is given in Table.
- “A” group has two subgroups namely “A1’ and “A2“. Similarly “AB” group has two subgroups namely “A1B” and “A2B”.
Determination Of The Abo Group: Determination of the ABO group is also called blood grouping, blood typing, or blood matching.
- Principle of Blood Typing – Agglutination: The blood typing is done on the basis of agglutination. Agglutination means the collection of separate particles like RBCs into clumps or masses. Agglutination occurs if an antigen is mixed with its corresponding antibody which is called isoagglutinin. Agglutination occurs when A antigen is mixed with anti-A or when B antigen is mixed with anti-B.
- Requisites for Blood Typing: To determine the blood group of a person, a suspension of his RBC and testing antisera are required. Suspension of RBC is prepared by mixing blood drops with isotonic saline (0.9%). The test sera are:
- Antiserum A, containing anti A
- Antiserum B, containing anti B.
- Blood Typing Procedure
- One drop of antiserum A is placed on one end of a glass slide (or a tile) and one drop of antiserum B on the other end
- One drop of RBC suspension is mixed with each antiserum. The slide is slightly rocked for 2 minutes. The presence or absence of agglutination is observed by the naked eyes and if necessary it is confirmed by using a microscope
- The presence of agglutination is confirmed by the presence of thick masses (clumping) of RBCs
- Absence of agglutination is confirmed by clear mixture with dispersed RBCs.
- Results Of Blood Typing
- If agglutination occurs with antiserum A: The antiserum A contains α antibody. The agglutination occurs if the RBC contains A antigen. So, the blood group is A.
- If agglutination occurs with antiserum B: The antiserum B contains β antibody. The agglutination occurs if the RBC contains B antigen. So, the blood group is B.
- If agglutination occurs with both antisera A and B: The RBC contains both A and B antigens to cause agglutination. And, the blood group is AB.
- If agglutination does not occur either with antiserum A or antiserum B: Agglutination does not occur if the RBC does not contain any antigen. The blood group is O.
Importance Of Abo Groups In Blood Transfusion
- During blood transfusion, only compatible blood must be used. The one who gives blood is called the donor and the one who receives the blood is called recipient.
- While transfusing the blood, antigen of the donor and the antibody of the recipient are considered. The antibody of the donor and antigen of the recipient are ignored mostly.
- Thus, RBC of the “O” group has no antigen and so agglutination does not occur with any other group of blood. So, ‘O’ group blood can be given to any blood group persons and the people of this group blood are called universal donors.
- The plasma of AB group blood has no antibodies. This does not cause agglutination of RBC from any other group of blood.
- The people of AB group can receive blood from any blood group person. So, people with this group blood are called universal recipients.
Matching And Cross Matching
- Blood typing (matching) is a laboratory test done to determine the blood group of a person. When the person needs blood transfusion, another test called cross matching is done after the blood is typed. It is done to find out whether the person’s body will accept the donor’s blood or not.
- For blood matching, RBC of the individual (recipient) and test sera are used. Cross-matching is done by mixing the serum of the recipient and the RBCs of donor. Cross-matching is always done before blood transfusion. If agglutination of RBCs from a donor occurs during cross-matching, the blood from that person is not used for transfusion.
Matching = Recipient’s RBC + Test sera Cross-matching = Recipient’s serum + Donor’s RBC
Inheritance Of Abo Agglutinogens And Agglutinins
- Blood group of a person depends upon the two genes inherited from each parent. Gene A and gene B are dominant by themselves and gene O is recessive. The Inheritance of blood group is represented schematically as given In Table.
- The antigens appear during the 6th month of fetal life. The concentration at birth is 1/5 of the adult concentration. It rises to the adult level at puberty. The antigens are present not only in RBCs but also present in many organs like salivary glands, pancreas, kidney, liver, lungs, etc.
- The A and B antigens are inherited from the parents as Mendelian phenotypes.
- The antibody a or p is not produced during fetal life. It starts appearing only two or three months after birth. Antibody is produced in response to A or B antigens which enter the body through respiratory system or digestive system along with bacteria.
- The antibodies are the gamma globulins which are mainly IgG and IgM immunoglobulins.
Transfusion Reactions Due To Abo Incompatibility
- Transfusion reactions are the adverse reactions in the body which occur due to transfusion error that involves transfusion of incompatible (mismatched) blood. The reactions may vary from fever and hives (skin disorder characterized by itching) to renal failure, shock, and death.
- In a mismatched transfusion, the transfusion reactions occur between the donor’s RBC and recipient’s plasma. So, if the donor’s plasma contains antibody against the recipient’s RBC, agglutination does not occur because these antibodies are diluted in the recipient’s blood.
- But, if the recipient’s plasma contains antibodies against the donor’s RBCs, the immune system launches a response against the new blood cells. Donor RBCs are agglutinated resulting in transfusion reactions.
- Severity of Transfusion Reactions: Severity of transfusion reactions varies from mild (fever and chills) to severe (acute kidney failure, shock, and death). The severity depends upon the amount of blood transfused, type of reaction, and the general health of the patient.
- Cause for Transfusion Reactions: Transfusion of incompatible blood produces hemolytic reactions. The recipient’s antibodies (IgG or IgM) adhere to the donor RBCs which are agglutinated and destroyed. Large amount of free hemoglobin is liberated into plasma. This leads to transfusion reactions.
- Signs and Symptoms of Transfusion Reactions:
- Nonhemolytic transfusion reaction: Nonhemolytic transfusion reaction develops within a few minutes to hours after the commencement of blood transfusion. Common symptoms are fever, difficulty in breathing, and itching.
- Hemolytic transfusion reaction: The hemolytic transfusion reaction may be acute or delayed. The acute hemolytic reaction occurs within few minutes of transfusion. It develops because of rapid hemolysis of the donor’s RBCs.
- Symptoms include fever, chills, increased heart rate, low blood pressure, shortness of breath, bronchospasm, nausea, vomiting, red urine, chest pain, back pain and rigor. Some patients may develop pulmonary edema and congestive cardiac failure.
- The delayed hemolytic reaction occurs from 1-5 days after transfusion. The hemolysis of RBCs results in release of large amount of hemoglobin into the plasma. This leads to the following complications.
- Jaundice: Normally, hemoglobin released from destroyed RBC is degraded and bilirubin is formed from it. When the serum bilirubin level increases above 2 mg/dL jaundice occurs.
- Cardiac Shock: Simultaneously, the hemoglobin released into the plasma increases the viscosity of blood. This increases the workload on the heart leading to heart failure. Moreover, toxic substances released from hemolyzed cells reduce arterial blood pressure and develop circulatory’ shock.
- Renal Shutdown
- The dysfunction of kidneys is called renal shutdown. The toxic substances from hemolyzed cells cause constriction of blood vessels in the kidney. In addition, the toxic substances along with free hemoglobin are filtered through glomerular membrane and enter renal tubules.
- Because of the poor rate of reabsorption from renal tubules, all these substances precipitate and obstruct the renal tubule. This suddenly stops formation of urine (anuria).
- If not treated with artificial kidney, the person dies within 10-12 days because of jaundice, circulatory shock, and more specifically due to renal shutdown and anuria.
Rh Factor
- Rh factor is an antigen present in RBC. The antigen was discovered by Landsteiner and Wiener. It was first iscovered in rhesus monkey and hence the name Rh factor. There are many Rh antigens but only the D is more antigenic in human.
- The persons having D antigen are called Rh positive and those without D antigen are called Rh negative. Among Asian population, 85% of people are Rh positive and 15% are Rh negative. The percentage of Rh-positive people is more among blacks (American blacks 95% and African blacks 100%).
- Rh group system is different from ABO group system because the antigen D does not have a corresponding natural antibody (anti D).
- However, if Rh-positive blood is transfused to a Rh-negative person for the first time, then anti-D is formed in that person. On the other hand, there is no risk of complications if Rh positive person receives Rh-negative blood.
Inheritance Of Rh Antigen: Rhesus factor is an inherited dominant factor. It may be homozygous Rhesus positive with DD or heterozygous Rhesus positive with Dd. Rhesus negative occurs only with complete absence of D (i.e. with homozygous dd).
Transfusion Reactions Due To Rh Incompatibility
- When a Rh-negative person receives Rh-positive blood for the first time, he is not affected much, since the reactions do not occur immediately. But, the Rh anlfcochss develop within one month. The transfused RBCs which are still present in the recipient’s blood, are agglutinated.
- These agglutinated cells are lysed by macrophages. So, a delayed transfusion reaction occurs. But, it is usually mild and does not affect the recipient.
- However, antibodies developed in the recipient remain in the body forever. So, when this person receives Rh-positive blood for the second time, the donor RBCs are agglutinated, and severe transfusion reactions occur immediately. These reactions are similar to the reactions of ABO incompatibility.
Hemolytic Disease Of Fetus And Newborn – Erythroblastosis Fetalis
- Hemolytic disease is a disease in fetus and newborns characterized by abnormal hemolysis of RBCs.
- It is due to Rh incompatibility, i.e. the difference between the Rh blood group of the mother and baby. The hemolytic disease leads to erythroblastosis fetalis.
- Erythroblastosis fetalis is a disorder in a fetus characterized by the presence of erythroblasts in blood. When a mother is Rh negative and fetus is Rh positive (the Rh factor being inherited from the father), usually the first child escapes the complications of Rh incompatibility.
- This is because the Rh antigen cannot pass from fetal blood into the mother’s blood through the placental barrier.
- However, at the time of parturition (delivery of the child) the Rh antigen from fetal blood may leak into mother’s blood because of placental detachment.
- During the postpartum period, i.e. within a month after delivery, the mother develops Rh antibody in her blood.
- When the mother conceives for the second time and if the fetus happens to be Rh positive again, the Rh antibody from mother’s blood crosses placental barrier and enters the fetal blood.
- Thus, the Rh antigen cannot cross the placental barrier whereas Rh antibody can cross it.
- The Rh agglutinins which enter the fetus cause agglutination of fetal RBCs resulting in hemolysis.
- The severe hemolysis in the fetus causes jaundice. To compensate the hemolysis of more and more RBCs, there is rapid production of RBCs, not only from bone marrow but also from spleen and liver. Now, many Large and immature cells in proerythroblastic stage are released into circulation.
- Because of this, the disease Is called erythroblastosis fetalis.
Ultimately due to excessive hemolysis severe complications develop, viz.
- Severe anemia
- Hydrops fetalis
- Kernicterus.
1. Severe Anemia: Excessive hemolysis results in anemia. And the infant dies when anemia becomes severe.
2. Hydrops Fetalis: It is a serious condition in fetus characterized by edema. Severe hemolysis results in the development of edema, enlargement of liver and spleen, and cardiac failure. When this condition becomes more severe it may lead to intrauterine death of fetus.
3. Kernicterus: Kernicterus is the form of brain damage in infants caused by severe jaundice. If the baby survives anemia in erythroblastosis fetalis then kernicterus develops because of high bilirubin content.
- The bloodbrain barrier is not well developed in infants as in adults. So, the bilirubin enters the brain and causes permanent brain damage.
- Most commonly affected parts of brain are basal ganglia, hippocampus, geniculate bodies, cerebellum, and cranial nerve nuclei. The features of this disease are:
- When the brain damage starts, the babies become lethargic and sleepy. They have high pitched cry, hypotonia, and arching of head backwards
- As the disease progresses, they develop hypertonia and opisthotonus
- The advanced signs of the disease are inability to suckle milk, irritability and crying, bicycling movements, choreoathetosis, spasticity, seizures, fever, and coma.
- Prevention or treatment for erythroblastosis fetalis
- If the mother is found to be Rh negative and the fetus is Rh positive, anti-D (antibody against D antigen) should be administered to the mother at the 28th and 34th weeks of gestation as a prophylactic measure.
- If a Rh-negative mother delivers a Rh-positive baby, then anti-D should be administered to the mother within 48 hours of delivery.
- This develops passive immunity and prevents the formation of Rh antibodies in mother’s blood. So the hemolytic disease of newborn does not occur in a subsequent pregnancy.
- If the baby is born with erythroblastosis fetalis, the treatment is given by means of exchange transfusion. Rh-negative blood is transfused into the infant replacing the infant’s own Rh-positive blood.
- It will now take at least 6 months for the infant’s new Rh-positive blood to replace the transfused Rh-negative blood. By this time all the molecules of Rh antibody derived from the mother get destroyed.
Other Blood Groups
In addition to ABO blood groups and Rh factor, many more blood group systems were found such as Lewis blood group and MNS blood groups. However, these systems of blood groups do not have much clinical importance.
1. Lewis Blood Group:
- This was first found in a subject named Mrs Lewis. The antibody that was found in this lady reacted with the antigens found on RBCs and in body fluids such as saliva, gastric juice, etc.
- The antigens, which are named Lewis antigens are formed in the tissues, released in the body secretions and then absorbed by the RBC membrane.
- Because of secretion along with body secretions, these antigens are also known as secretor antigens. Presence of Lewis antigens in children leads to some complications such as retarded growth. Sometimes, it causes transfusion reactions also.
2. MNS Blood Groups: The MNS blood groups are determined by their reactions with anti-M, anti-N, and anti-S. However, these blood groups rarely cause any trouble like hemolysis following transfusion.
3. Other Blood Groups: Other blood groups include
- Auberger groups
- Diego group
- Bombay group
- Duffy Group
- Lutheran group
- P group visit Kell group
- I group
- Kidd group
- Suiter Xg group.
Importance Of Knowing Blood Group
- Nowadays, knowledge of blood group is very essential medically, socially, and judicially. The importance of knowing the blood group is:
- Medically, it is important during blood transfusions and in tissue transplants
- Socially, one should know his or her own blood group and become a member of the Blood Donor’s club so that he or she can be approached for blood donation during emergency conditions
- It general among couples, knowledge of blood groups helps to prevent complications due to Rh incompatibility and save the child from the disorders like erythroblastosis fetalis
- Judicially, it is helpful in medicolegal cases to sort out parental disputes.
Leave a Reply