Immunohematology (Blood Bank Testing) Flashcards
H Antigen
considered the foundation onto which both A & B antigens are created
Bombay Phenotype
Rare phenotype without even the H antigen
How do antigens attach to the RBC surface?
ABO blood group antigens are attached to oligosaccharide chains that project above the RBC surface. These chains are attached to lipids that lie in the RBC membrane
3 Features of Antibodies’ Clinical Significance
Antibodies destroy RBCs in vivo, cause HDN, and are common.
Types of Autoimmune Hemolytic Anemias
Warm-reactive autoantibodies. Cold-reactive autoantibodies: cold hemagglutinin dz, Paroxysmal cold hemoglobinuria
Types of Alloimmune Hemolytic Anemias
Hemolytic dz of the newborn (HDN), Hemolytic transfusion reactions.
Third type of Immune Hemolytic Anemia
Drug Induced
Autograft
Tissue from a person’s own body being replaced. (Blood removed and returned, a vein from the leg being used in the neck.
Allograft
A same-species transplant. Most organ transplants or blood transplants.
Xenograft
Inter-species transplant
What is unique about AB antibodies?
They are the ONLY system wherein the reciprocal antibodies are consistently and predictably present in the sera of people who have had no exposure to human red cells! (Usually exposure is required to make antibodies.
Most important Blood Group system for transfusion practice?
ABO. Also the first to be identified.
Isohemaglutinins
Naturally occurring antibodies & complete antibodies (IgM class) against A & B antigens.
ABO antibodies
IgM large enough to produce visible agglutination. Formed w/out prior sensitization to the foreign RBC. Thought to have formed from encountering similar antigenic determinants on micro-organisms.
ABO Blood types & their corresponding antibodies
Type A -> B antibody. Type B -> A antibody. Type AB -> no antibody. Type O -> A & B antibodies.
What are the three tests that must be performed every time there is a transfusion?
Forward Grouping, Reverse Grouping, Crossmatching.
Forward Grouping
Reaction of patient’s red blood cells (unknown) with Reagent anti-A & anti-B antisera (known)
Reverse Grouping
Reaction of patient serum (unknown) with reagent Group A & Group B cells (known)
Crossmatching
Last step before transfusion. Mix donor RBC w/recipient’s plasma & test for rxn.
HDN: Hemolytic Dz of the Newborn
AKA Erythroblastosis fetalis. Occurs secondary to trans-placental transfer of maternal antibodies. Most commonly, RH incompatibility (“could” be ABO). Rh HDN occurs with an Rh (-) mother, Rh (+) father, firstborn OK, in subsequent babies affected after the mother’s been sensitized. Anti D antibodies are IgG, and are able to pass across the placenta.
Tx for HDN
Mother immunized with RhoGam (Rh immune globulin).
Rh factors: Fisher-Race Theory
Allelic genes: Dd, Cd, and Ee. Antigens: Cc, D, Ee. **NO “d” ANTIGEN! Rh (+) persons are D antigen (+), Rh negative persons are D (-), no “d” has been discovered. D is the most antigenic of this group, Anti-D IgG is a STRONG antibody!
Only 2 ways for an Rh- person to express Rh antibodies
Placental sensitization, transfusion.
D’u’
2-3% of people initially appearing Rh (-) are actually D’u’ (+). In serum testing Anti-D reagents coat the weak D cells but no visible agglutination occurs. Screening for Weak D involves adding Anti-Human Globulin, an indirect antiglobulin test.