ABO Blood Group System PDF

ABO Blood Group System 1 Prepared by: Basma Samir (MD) Blood group system A set of antigens exhibiting similar serological and physiological Prepared by: Basma Samir (MD) characteristics, and inherite...

ABO Blood Group System 1 Prepared by: Basma Samir (MD) Blood group system A set of antigens exhibiting similar serological and physiological Prepared by: Basma Samir (MD) characteristics, and inherited according to a specific pattern. 2 The ABO system  ABO IgM antibodies are produced in the first years of life by sensitization to environmental substances such as food, bacteria, and viruses. Prepared by: Basma Samir (MD)  The "O" in ABO is often called "0" (zero/null) in other languages 3 Importance of the ABO system Most important (clinically significant) Blood Group System for transfusion practice Why? The only blood group system in which antibodies are Prepared by: Basma Samir (MD) consistently, predictably, and naturally present in serum of people who lack the antigen. They need no previous exposure. Naturally occurring A and B antibodies are IgM and can readily activate complement and cause hemolysis and possibly death. A single RBC carries (800,000 – 2 Million) ABO antigens. Therefore ABO compatibility between donor and recipient is crucial because of these strong naturally occurring Abs. 4  Characteristics of ABO Ags ABO antigens are glycolipid in nature (oligosaccharides) attached directly to lipids on red cell membrane. They stick out from red cell membrane. Besides their presence on red blood cells, soluble Prepared by: Basma Samir (MD) antigens can be present in plasma, saliva, and other secretions in secretors. They are also expressed on tissues other than red cells. This last fact is important to consider in organ transplantation. ABO Ags are only moderately well developed at 5 birth. Therefore ABO-HDN not as severe as other kinds of Hemolytic Disease of the Newborn. ABO blood group system- diagram showing the carbohydrate chains that determine the ABO blood group Prepared by: Basma Samir (MD) 6  Prepared by: Basma Samir (MD) 7 Function of the A & B antigens The functions of the ABO blood group antigens are not known. Prepared by: Basma Samir (MD) Individuals who lack the A and B antigens are healthy, suggesting that any function the antigens have is not important, at least not in modern times. 8 Characteristics of ABO Abs These are expected naturally occurring antibodies that occur without exposure to red cells containing the antigen. Immunoglobulin M antibodies, predominantly They react in saline and readily agglutinate. Prepared by: Basma Samir (MD) Their optimum temperature is less than 30oC, but reactions do take place at body temperature They are absent at birth and start to appear around 3-6 months as result of stimulus by bacterial polysaccharides. (For this reason, 9 newborn blood is only forward typed.)  ABO INHERITANCE Prepared by: Basma Samir (MD) 10 ABO Genes The A and B genes found on chromosome # 9. We inherit one gene (allele) from father and one from mother. The two co-dominant alleles are A or B. Anytime Prepared by: Basma Samir (MD) an individual inherits an A or B gene it will be expressed. The O gene signifies lack of A or B antigens. It is not expressed unless this gene is inherited from both parents (OO). Therefore the O gene is 11 recessive. Inheritance Patterns A/A parent can only pass along A gene Prepared by: Basma Samir (MD) A/O parent can pass along either A or O gene B/B parent can only pass along B gene B/O parent can pass along either B or O gene O/O parent can only pass along O gene AB parent can pass along either A or B gene 12 Inheritance Patterns ABO phenotypes and genotypes Prepared by: Basma Samir (MD) 1. Group A phenotype = A/A or A/O genotype 2. Group B phenotype = B/B or B/O genotype 3. Group O phenotype = O/O genotype 4. Group AB phenotype = A/B genotype 13 Production of A, B, and H antigens The production of A, B and H antigens are controlled by the action of transferases. Prepared by: Basma Samir (MD) These transferases are enzymes that catalyze (or control) addition of specific sugars to the oligosaccharide chain. The H, A, or B genes each produce a different transferase, which adds a different specific sugar to the oligosaccharide chain. 14 Expression of ABO Ags Although the ABO blood group antigens are regarded as RBC antigens, they are actually expressed on a wide variety of human tissues and are present on most epithelial and endothelial cells. Prepared by: Basma Samir (MD) Each human RBC expresses (800,000 - 2 million) ABO blood group antigens. Other blood cells, such as T cells, B cells, and platelets, have ABO blood group antigens that have been adsorbed from the plasma. 15 Expression of ABO Ags In individuals who are "secretors", a soluble form of the ABO blood group antigens is found in saliva and Prepared by: Basma Samir (MD) in all bodily fluids except for the cerebrospinal fluid. 16 Expression of ABO Ags  A number of illnesses may alter a person's ABO phenotype.  Patients can "acquire" the B antigen during a necrotizing infection during which bacteria Prepared by: Basma Samir (MD) release an enzyme into the circulation that converts the A1 antigen into a B-like antigen.  During this time, patients should not receive blood products that contain the B antigen because their sera will still contain anti-B.  Once the underlying infection is treated, the 17 patients' blood groups return to normal. Expression of ABO Ags  Illness can also cause patients to "lose" ABO blood group antigens.  Any disease that increases the body's demand for Prepared by: Basma Samir (MD) RBCs may weaken the expression of ABO blood group antigens, e.g., thalassemia.  In addition, ABO blood group antigens can be altered by hematological cancers that can modify the sugar chains that bear the ABO blood group 18 antigens. Bombay blood group: The Bombay blood group lacks H gene and therefore cannot make H antigen (H substance). Since the H substance is the precursor for the A and Prepared by: Basma Samir (MD) B antigens, these antigens also are not made. The cells type as O and the serum has anti-A, anti-B, and anti-H since the individual lacks all of these antigens. 19 Subgroups of A and B Most of the other 20% are either A2 or A2B. There are other, weaker subgroups of A: Prepared by: Basma Samir (MD) A3; Aint; Am, Ax; Ael. Each has a different pattern of reacting with anti-A, anti-A, and various antibody-like substances called lectins. 20 Secretors The Se locus (FUT2) Located on chromosome 19. The Se locus encodes a specific fucosyltransferase that is expressed in the epithelia of secretory tissues, such as salivary glands, the gastrointestinal tract, and the respiratory tract. Prepared by: Basma Samir (MD) "Secretors" have at least one copy of the Se gene—their genotype is Se/Se or Se/se. They secrete H antigen which, depending on their ABO genotype, is then processed into A and/or B antigens. Non-secretors are homozygous for null alleles at this locus (se/se). Non-secretors are unable to produce a soluble form of H 21 antigen and hence do not produce A and B antigens. INDICATIONS FOR ABO GROUPING Prepared by: Basma Samir (MD) 22  Blood Donors-since it can be life threatening to transfuse the wrong ABO group. Transfusion recipients-since we need to know the donor blood is ABO compatible. Organ Transplant Candidates and Donors-ABO antigens are found in other tissues as well. Therefore the transplant candidates and donors must be compatible. Prenatal Patients-To determine whether the mothers may have Prepared by: Basma Samir (MD) babies who are suffering from ABO-HDN. Newborns (sometimes) If the baby is demonstrating symptoms of Hemolytic Disease of the Newborn, the ABO group needs to be determined along with Rh and others. Paternity testing Since the inheritance of the ABO Blood Group System is very specific, this serves as one of the first methods 23 to determine the likelihood that the accused father is the father or not. ABO Typing ABO typing involves both antigen typing and antibody detection. Prepared by: Basma Samir (MD) The antigen typing is referred to as the forward typing, and the antibody detection is the reverse typing. 24 ABO Typing The forward typing determines antigens on patient's or donor's cells a. Cells are tested with the antisera reagents anti- A, anti-B Prepared by: Basma Samir (MD) b. Reagents are either made from hyperimmunized human sources, or monoclonal antibodies. c. Advantages of monoclonals: Strong, besides human source reagents can transmit infectious disease (hepatitis). 25 ABO Typing Reverse typing determines antibodies in patient's or donor's serum or plasma Prepared by: Basma Samir (MD) a. Serum tested with reagent A1 cells and B cells b. Reverse grouping is also known as backtyping or serum confirmation 26  Prepared by: Basma Samir (MD) 27 Discrepancies in ABO typing Results of forward and reverse typing must agree before reporting out blood type as seen in the about table. Prepared by: Basma Samir (MD) If forward and reverse do not agree, must identify cause of discrepancy. If cannot resolve discrepancy, must report out blood type as UNKNOWN 28 and give group O blood Subgroups of A and B Subgroups of A and B are caused by decreased amounts of antigen on the red blood cells. Prepared by: Basma Samir (MD) They are inherited conditions. The most common are subgroups of A. Approximately 80% of the A's and AB's have a normal expression of A1. 29 Lectins Lectins are extracts of seeds of plants that react specifically with certain antigens. The two most common lectins used in Blood Bank Prepared by: Basma Samir (MD) are: Ulex europaeus, or lectin H, which agglutinates cells that have H substance. Dolichos biflouros, or lectin A1, which agglutinates 30 cells with A1. Red blood cell compatibility Blood group A individuals have the A antigen on the surface of their RBCs, and blood serum contains IgM antibodies against the B antigen. Prepared by: Basma Samir (MD) 31 Red blood cell compatibility Blood group B individuals have the B antigen on the surface of their RBCs, and blood serum containing IgM antibodies against the A antigen. Prepared by: Basma Samir (MD) 32 Red blood cell compatibility Blood group AB individuals have both A and B antigens on the surface of their RBCs, and their blood serum does not contain any antibodies against either Prepared by: Basma Samir (MD) A or B antigen. 33 Red blood cell compatibility Blood group O (or blood group zero in some countries) individuals do not have either A or B antigens on the surface of their RBCs, Prepared by: Basma Samir (MD) but their blood serum contains BOTH IgM anti-A antibodies and anti-B antibodies against the A and B blood group antigens. 34 Red blood cell compatibility If anyone needs a blood transfusion in a dire emergency, and if the time taken to process the Prepared by: Basma Samir (MD) recipient's blood would cause a detrimental delay, O Negative blood can be issued. 35 Diseases associated with ABO blood group antigens No diseases are known to result from the lack of expression of ABO blood group antigens, but the susceptibility to a number of diseases has been Prepared by: Basma Samir (MD) linked with a person's ABO phenotype. Such correlations remain controversial and include the observation that ▪ gastric cancer appears to be more common in group A individuals, ▪ whereas gastric and duodenal ulcers occur more 36 often in group O individuals. Clinical significance of ABO antibodies ABO antibodies are of major clinical significance for these reasons: Prepared by: Basma Samir (MD) They are naturally occurring and are Found universally, and They are highly reactive. 37 Clinical significance of ABO antibodies Transfusion reactions The routine practice of blood typing and cross matching blood products should prevent adverse transfusion reactions Prepared by: Basma Samir (MD) caused by ABO antibodies. However, clerical error can result in "the wrong blood" being transfused into a patient, an error which can result in the 38 death of the patient.  Clinical significance of ABO antibodies Transfusion reactions If a recipient who has blood group O is transfused with non-group O RBCs, the naturally occurring anti-A and anti-B in the recipient's serum binds to their Prepared by: Basma Samir (MD) corresponding antigens on the transfused RBCs. These antibodies fix complement and cause rapid intravascular hemolysis, triggering an acute hemolytic transfusion reaction that can cause disseminated intravascular coagulation, shock, acute renal failure, and death. Anti-A1 is a less significant cause of transfusion 39 reactions and does not appear to fix complement. Hemolytic disease of the newborn HDN tends to be relatively mild in nature mainly because fetal RBCs don't express adult levels of A and Prepared by: Basma Samir (MD) B antigens. However, the strength of fetal ABO blood group antigens can vary, and therefore the degree of hemolysis and hence the severity of HDN can be unpredictable. 40