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TYPE & SCREEN

TYPE & SCREEN. What does the Blood Bank Do with That Tube?. Blood group Antigens. Markers on various red cell structures Detected by serologic techniques Antigens organized into 26 blood group systems that segregate independently Multiple alleles within each system

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TYPE & SCREEN

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  1. TYPE & SCREEN What does the Blood Bank Do with That Tube?

  2. Blood group Antigens • Markers on various red cell structures • Detected by serologic techniques • Antigens organized into 26 blood group systems that segregate independently • Multiple alleles within each system • Complete red cell phenotypes are highly individualized

  3. The Nature of Red Cell Antigens • Proteins & sugars on surface of RBC vary slightly in different individuals • Protein antigen direct product of gene • Carbohydrate antigen indirect product of the defining gene • Encoded transferase enzymes attaches an immunodominant sugar to a cell membrane component

  4. The Nature of Red Cell Antigens • Packed on the surface innumerable antigens • Type A cell has 1 x 106 A antigen sites • 800,000 MN antigen sites • 150,000 SsU antigen sites • 20,000 Rh antigen sites • Hundreds of additional known antigen sites • Number of antigens no clinical correlation • 800,000 MN sites vs 4000 Kell sites

  5. Recognition of Blood Groups • Recognition begins with discovery of an antibody • Likely that after a century of blood group research all of the major human blood group systems have been discovered

  6. ABO Testing

  7. ABO Testing • Front Type • PT RBCs  Anti-A or Anti-B Abs • Back Type • A or B RBCs  PT Serum/Plasma

  8. Table 3-1. Reaction of O, A, B, and AB Groups

  9. Table 2-3. ABO Blood Group Antigens and Antibodies

  10. Table 2-2. Frequency (%) of ABO Blood Groups in the United States

  11. Blood Group Antibodies

  12. IgG Binds with Ag @ 37° Fc portion carries macrophage receptor 2 Fab sites Monomer requires high concentration to activate complement, only to C3 Amplifies extravascular hemolysis IgM Binds with antigen at ambient temperature or colder 10 Fab sites Polymer allows complement activation to C9 Intravascular hemolysis if reactive at 37° Blood Group Antibodies

  13. Polyclonal Multiple cell lines with different specificities Monoclonal Single Antibody specificity Polyspecific Contains both anti-IgG and anti-complement Monospecific Contains either anti-IgG or anti-complement Antihuman Globulin (AHG) Reagents

  14. Direct Antiglobulin Test (DAT) • Detects antibody bound to RBCs in vivo • Diagnostic test • Performed only when clinical evidence suggests • Autoimmune hemolytic anemia • Hemolytic disease of the newborn • Hemolytic transfusion reaction • Monospecific reagents used to specify immunoglobulin • One-step test

  15. Indirect Antiglobulin Test (IAT) • Detects free antibody in serum • Method for pretransfusion antibody detection • AHG reagent must contain anti-IgG • Two step test – Ag/Ab binding occurs in vitro • Other applications: antibody identification, extended antigen typing, weak D test

  16. Selection of Donor ABO Type • From the perspective of reactions to blood transfusion caused by Ag-Ab reactions, only antibodies matter • Antigens on donor red cells are of no immediate consequence in the absence of antibody • Therefore ABO blood group system is of particular clinical importance

  17. Blood Group Immunizations: Most Common Specificities • Rh • Kell • Duffy • Kidd • MNSs

  18. Blood Group Immunization:Determining Factors • Immunogenic potential of antigen • Rh and Kell most potent • Dose of antigen • Amount and frequency of exposure • Immunocompetence of recipient • Diagnosis: 20% non-responder rate • Immunization occurs in approximately 1% of transfusions and 5% of transfused patients

  19. Rh Typing • D antigen is potent immunogen • 50% Rh - given 1 unit of Rh+ make anti-D • However, 30% are non-responders despite repeated Rh+ transfusions • Anti-D may cause serious reactions with Rh+ transfusion • Most dangerous of all blood group antibodies in severe HDN

  20. Other Blood Donor Antigens • K antigen of the Kell blood group system 2nd to Rh in potential to provoke antibody response • 5% K- given one unit of K+ blood make anti-K • But frequency of K is only 9% in whites and lower in Black and Hispanic individuals • Some services attempt donor selection Rh (c and E), Kidd (Jka), and some others

  21. Compatibility Tests • ABO Type • Rh Type • Antibody Detection (Screen) • Antibody Identification • Crossmatch • Saline • Coombs

  22. Crossmatch • Immediate Spin Crossmatch • Usual • Room Temperature • Full Crossmatch • Antibody Screen Positive • Prior History Antibodies • Room Temperature • 37° • AHG (Coombs)

  23. Table 31-11 ABO and Rh (D) Compatibility in Blood Transfusion S=Substitute as packed red blood cells or wash to eliminate antibodies. E = Only under extreme emergency conditions, especially if the recipient is a young female.

  24. Table 31-12 Probability of Safe Blood Transfusion

  25. Table 31-8 Approximate Time Required for Preparing for a Blood Transfusion

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