5. Blood group & typing.pdf

BLOOD GROUP AND TYPING MBBS & BDS 1 Dr. Lindani Chirwa Haematology Unit Pathology Department  OBJECTIVES Name the two main blood group systems Explain why ABO system is the most important for transfusion therapy Describe the pathogenesis...

BLOOD GROUP AND TYPING MBBS & BDS 1 Dr. Lindani Chirwa Haematology Unit Pathology Department  OBJECTIVES Name the two main blood group systems Explain why ABO system is the most important for transfusion therapy Describe the pathogenesis of haemolytic disease of the foetus & newborn (HDFN) List three essential steps in blood compatibility testing  INTRODUCTION The ability to detect & identify blood group antigens and antibodies is key to safe & life-saving blood transfusion. Exposure to erythrocytes carrying an antigen lacking on the recipient’s RBCs can elicit an immune response Blood group antigens are important in  Allogeneic blood transfusion  Maternofetal blood group incompatibility  Organ transplantation  KEY TERMS  Antigen – any substance that, when introduced into a body and recognized as foreign, will elicit an immune response. Antibody – a product of an immune response.  Usually react specifically with a certain antigen in some observable way Agglutination – clumping of red cells caused by an antibody attaching to antigens on more than one red cell Alloimmunization – immune response from non-self antigens from the same species e.g. blood transfusion. Alloimmunization is the process by which a person's immune system becomes sensitized to antigens from another individual of the same species, typically after exposure to foreign red blood cells, platelets, or other tissues. Immunogenicity – ability to stimulate antibody production.  Depends on antigen size, complexity & dose.  BLOOD GROUP SYSTEMS & ANTIGENS  Polymorphic, inherited, carbohydrate/protein structures located on outside surface of RBC membrane. There are at least 29 known blood group systems  9 are considered major  ABO, Rh, MNS, P, Kell, Duffy, Kidd, Lewis & Lutheran Approximately 400 red blood cell group antigens have been described (these are within the 29 systems) Clinical significance in blood transfusion  Individuals who lack a particular blood group antigen may produce antibodies reacting with that antigen  This leads to a transfusion reaction  BLOOD GROUP SYSTEMS & ANTIGENS  Different blood group antigens vary in their clinical significance ABO & Rh groups are the most important Other blood groups are of less clinical importance:  Some react at low temperature e.g. Lewis, MN system  Many are of low antigenicity  Occur in relatively low frequency e.g. Kell These may be significant in patients receiving multiple transfusions  E.g. Sickle Cell Disease & Thalassaemia  May cause delayed haemolytic reaction CLINICALLY SIGNIFICANT BLOOD GROUP SYSTEMS  BLOOD GROUP ANTIBODIES  Two types Natural antibodies  Thought to develop in the early weeks to months of life (neonatal to infancy) through exposure to bacteria & other antigens similar in structure  ABO anti-A & anti-B being the clinically significant  Usually immunoglobulin M (IgM) Immune antibodies  Develop in response to transfusion or transplacental passage during pregnancy  Commonly IgG  Rh antibody, anti-D is the clinically significant example  ABO SYSTEM  The most important in transfusion Alloagglutinins are normally present in the absence of corresponding antigen  Strong fatal reactions occur when incompatible blood is transfused ABO genes are located on chromosome 9 Controlled by 3 alleles: A, B & O  O is recessive to A & B alleles which are co-dominant ABO phenotype is shown by grouping laboratory tests on a blood test  THE ABO SYSTEM PHENOTYPE GENOTYPE ANTIGENS ANTIBODIES FREQUENCY IN MALAWI (%) O OO None Anti-A, Anti-B 50 A AA or AO A Anti-B 24 B BB or BO B Anti-A 22 AB AB AB None 4  Rh SYSTEM Rh group locus is composed of two related structural genes, RhD & RhCE It has 5 antigens; D, C, c, E, e RhD being the most clinically significant  The RhD gene may be present; RhD positive or absent RhD negative  Rh antibodies are immune antibodies that result from previous transfusion or pregnancy  COMPATIBILITY TESTING  The following are the steps performed in the lab: i. ABO & RhD Grouping on patient ii. Antibody screening on patient iii. Cross-matching between patient serum and donor red blood cells  Agglutination Sometimes when an antibody reacts with an antigen that is located on a red cell, the red cells are clumped together. This clumping is termed agglutination. Anti-A will agglutinate red cells with A antigens on them. Anti-B will agglutinate red cells with B antigens on them. These reactions will determine the blood group. Slide 13  TECHNIQUES IN BLOOD GROUP SEROLOGY  Most important technique based on agglutination of red blood cells Four common methods  Slide/tile method  Tube test  Microplate technology  Column or gel centrifugation  ABO GROUPING  Forward grouping – typing red cells for the presence/absence of antigen A or B Reverse grouping– testing the serum/plasma for presence or absence of anti-A and/or Anti-B antibodies Forward & reverse grouping results should correlate  Landsteiner’s rule CROSSMATCH  BLOOD TRANSFUSION Ideally it is good to transfuse with same ABO group (ABO identical) However, that may not be feasible/practical Blood group O is a universal donor as  They do not have antigen A or B on their surface to react with antibodies within the circulation of the recipient  Usually the Anti-A & Anti-B are in low titre (easily diluted by recipient plasma) & therefore not harmful Blood group AB is a universal recipient  They lack antibodies to react with recipient red cells  Usually plasma from the donor has low titre to react with A & B antigens BLOOD TRANSFUSION  HAEMOLYTIC DISEASE OF THE FETUS AND NEWBORN (HDFN) HDFN occurs when the mother has IgG red cell alloantibodies in her plasma  These cross the placenta and bind to corresponding antigen on fetus red cells  Immune haemolysis may cause variable degree of fetal anaemia  In severe cases fetus may die in-utero due to heart failure (hydops fetalis)  After delivery, affected babies may present with jaundice within 24 hours  May cause neurological damage The most important red cell alloantibodies in clinical practice are:  RhD (anti-D)  Rhc (anti-c)  Kell (anti-K) – causes suppression of haematopoiesis, rather than haemolysis  HAEMOLYTIC DISEASE OF THE FETUS AND NEWBORN (HDFN)  Red cell alloantibodies (sensitization) may occur as a result of:  Previous pregnancy where fetal blood containing paternal antigens RhD + cross the placenta (to mix with RhD negative mother’s blood) Usually at delivery & third trimester  Blood transfusion – RhD negative receiving RhD + blood HDFN then happens at subsequent RhD + pregnancy  Secondary immune response leading to increased maternal IgG anti-D which can cross the placenta Causes an increased perinatal mortality without prophylaxis  HAEMOLYTIC DISEASE OF THE FETUS AND NEWBORN (HDFN)  Routine antenatal anti-D prophylaxis is recommended in RhD negative pregnant women  2-doses regimen: at 28 & 34 weeks of gestation  Single-dose regimen: between 28-30 weeks Prophylaxis is also given within 72 hours of giving birth to a RhD positive baby  REFERENCES Hoffbrand, Haematology at a Glance, 4th edition. Hoffbrand, Essential Haematology, 7th Edition Dr. Norfolk, Handbook of Transfusion Medicine, 5th Edition Hillyer, Blood Banking & Transfusion Medicine The End.