SI2101 Haematology Lecture 3: Blood Groups PDF

SI2101: Haematology Lecture 3: Blood Groups Dr. Louise Horrigan Physiology [email protected] University ofGalway.ie Learning To learn: Concept of blood groups Objectiv...

SI2101: Haematology Lecture 3: Blood Groups Dr. Louise Horrigan Physiology [email protected] University ofGalway.ie Learning To learn: Concept of blood groups Objectives of ABO blood group system Today’s Lecture Inheritance inheritance Expression of antigens and production of antibodies Blood transfusions Compatability Haemolytic reactions Rhesus system Haemolytic Disease of the Newborn Antibodies in plasma Antigens on surface of (agglutinins) erythrocytes (agglutinogens) Blood group systems 36 blood group ‘systems’ identified to date ABO, Rhesus, Kell, Duffy, Kidd………. 346 different antigens across all systems ABO and Rhesus are the most important clinically ABO consists of 2 antigens – A and B Rhesus consists of 50 antigens in total but D is the most important clinically University ofGalway.ie ABO antigens = A antigen = B antigen Type A blood Type B blood Type AB blood Type O blood ABO antibodies An antibody is ‘specific’ for a particular antigen There are 2 types of agglutinins in the ABO system: anti-A and anti-B antibodies We have agglutinins in our plasma that are specific for the agglutinogen(s) that we do not have A person with Type A blood will have anti-B antibodies A person with Type B blood will have anti-A antibodies A person with Type AB blood will have neither anti-A nor antiB antibodies A person with Type O blood will have both anti-A and anti-B antibodies University ofGalway.ie ABO inheritance Which blood type am I? Depends on which alleles (gene variations) you inherit The ABO system is governed by 3 alleles: A allele codes for an enzyme that produces the A antigen B allele codes for an enzyme that produces the B antigen O allele codes for an enzyme that is non-functional and produces no antigen Each person inherits one allele from each parent A and B are dominant, O is recessive University ofGalway.ie Genotype Blood Type AA A AB AB BB B AO A BO B OO O Blood transfusions Blood types discovered by Karl Landsteiner in Austria Father of transfusion medicine Won Nobel Prize in Physiology or Medicine in 1930 A ‘wrong’ transfusion –Example: If anti-A antibodies from one person come in contact with the A antigen on erythrocytes from a person with Type A or Type AB blood, agglutination (clumping) of erythrocytes can occur University ofGalway.ie If blood from two ‘incompatible’ people are mixed………… Agglutination occurs, followed by haemolysis! A antigen from Person 1 Y Anti-A antibody from Person 2  Donated blood processed to produce different components Packed red blood cells, leukocytes, platelets, plasma, cryoprecipitate Limit unnecessary exposure to blood components and optimise usability Compatibility testing performed between donor and recipient blood Antibody screen and Cross-matching Universal donor/recipient for RBC transfusions Universal donor: blood group O Red blood cells can be given but not plasma Universal recipient: blood group AB Cross-matching required for other blood group antigen incompatibilities Who can donate RBCs to who? Donor Recipient A A B B AB AB O O Rhesus system 50 different antigens exist, 5 considered important D, C, E, c, e D (Rhesus factor) most important When a person has the D antigen on their erythrocytes, they are rhesus positive Person’s ABO and Rh blood group reported together A+, A-, B+, B- etc. Inheritance is governed by the D allele (and the lack of the D allele) A Rhesus positive person may be heterozygous or homozygous for the D allele Prevalence of the D antigen varies with ethnicity 15% of white people are Rhesus negative 5 – 8% of African-Americans are Rhesus negative University ofGalway.ie 1 – 2% of Asians, Africans and Native Americans are Rhesus negative When are anti-D antibodies produced? 1. If aRhperson receives a blood transfusion of - Rh+ blood 2. When a Rh mother gives birth to a Rh baby - + Unlike the ABO system, antibodies to the D antigen are NOT generally present in a rhesus negative person University ofGalway.ie  Haemolytic disease of the newborn (erythroblastosis fetalis) Due to blood type incompatibility between mother and foetus Mainly associated with the rhesus (D) antigen Baby’s erythrocytes leak in to mother’s system Mainly during labour, possibly during pregnancy Provoke antibody generation in the mother to D antigens on RBCs (anti-D antibodies) Anti-D antibodies can cross the placenta during subsequent pregnancies and bind foetal erythrocytes Causes agglutination of erythrocytes in infant, leading to blockage of blood vessels, and haemolysis First baby usually unharmed Risk increases with subsequent pregnancies University Anti-D antibodies are of the IgG type, which can easily cross the placenta. ofGalway.ie This image is licensed under the Creative Commons Attribution 3.0 Unported license. Source: Anatomy & Physiology, Connexions Website. http://cnx.org/content/col11496/1.6/, Jun 19, 2013. Author: OpenStax College Effects in baby range from mild anaemia to hydrops fetalis (fluid accumulation leading to severe oedema, HCT < 5, 50% mortality) Haemolysis leading to jaundice, kernicterus (bilirubin in brain) Possible death Image from pxfuel.com, under a Creative Prevention Commons License –RhoGam (anti-D) antibody treatment given prophylactically at 28 weeks and/or administered within 72 hrs after birth Believed to bind to the D antigen on any of the baby’s RBCs that enter the mother’s system, and thus marks the cells for clearance by mother’s immune system –Use of RhoGam postnatally (introduced in 1968) reduced the incidence from 1% worldwide to 0.5% –Later, the introduction of antenatal RhoGam further reduced the incidence to 0.1% –An estimated 1 - 3 in 1000 Rh- women still develop alloimmunization worldwide Summary of Main Points Blood groups relate to the antigens expressed on the surface of red blood cells, that can bind to antibodies produced by another person Two families of blood groups clinically most important – ABO and Rhesus Inheritance of antigens of ABO system governed by 3 alleles – A, B and O – giving rise to 4 ABO blood groups (A, B, O, AB) Within the ABO system, people carry antibodies to the antigens that they do not express themselves Rhesus +ve and –ve relate to the presence or absence of the D antigen Unlike ABO, Rh- people do not usually carry antibodies to the D antigen Mixing of incompatible blood groups (eg. wrong transfusion) leads to haemolytic reactions that can be fatal Haemolytic Disease of the Newborn can occur when a Rh- mother gives birth University to a Rh+ baby ofGalway.ie RhoGam