L26 – Transfusion beyond Immunohaematology Flashcards
2 ways of grouping blood types by ABO?
- Cell grouping: presence/absence of A, B antigen(s) on the RBC’s
- Plasma / serum grouping: presence/absence of Anti-A &/or Anti-B in serum
What does the ABO gene code for? Which chromsome?
chromosome 9.
code for enzyme with glycosyltransferase activity
> > modifies oligosaccharides on glycoproteins at surface membrane of RBC
Compare the effects of glycosyltransferace on different ABO blood groups?
Default oligosaccharide structure = H-antigen
A allele = adding N-acetyl galactosamine to H-antigen = A Antigen
B allele = adding galactose to H antigen = B antigen
O allele = protein with loss of transferase activity = H antigen
What type of Ig is natural Anti-A, Anti-B antibodies? Can it cross placenta?
IgM
active at body temperature
Cannot cross placenta
How does Anti-A, Anti-B Ab cause hemolysis of incompatible RBCs?
Anti-A/B IgM can activate complements at body temp»_space; acute intravascular hemolysis
Difference between natural and immune-induced Anti-A/ Anti-B Antigen?
Natural = IgM
Immune origin = IgG
Inheritance pattern of ABO gene?
Autosomal dominant
Define the A,B antigen and Anti-A, Anti-B antibodies in Group O blood?
No A,B antigen
Have both Anti-A, Anti-B Ab
Define the A,B antigen and Anti-A, Anti-B antibodies in Group A blood?
Have A antigen
Have Anti-B Ab
Define the A,B antigen and Anti-A, Anti-B antibodies in Group B blood?
Have B antigen
Have Anti-A Ab
Define the A,B antigen and Anti-A, Anti-B antibodies in Group AB blood?
Have both A, B antigen
No Anti-A or Anti-B Ab
List the genotypes that correspond to A,B,AB and O group blood.
Group A = AA, AO
Group B = BB,BO
Group AB = AB
Group O = OO
List 2 conditions due to ABO incompatibility
Acute haemolytic transfusion reaction
ABO haemolytic disease of the newborn (HDN)
Pathogenesis of acute hemolytic transfusion reaction?
Natural Anti-A/B Ab bind to incompatible RBC
Activate complements»_space; acute intravascular haemolysis
Symptoms of acute hemolytic transfusion reaction?
Fever
Hemoglobinemia (free Hb)
Hemoglobinuria (should differentiate from hematuria by urine microscopy)
Hemosiderinuria
DIC = multiorgan failure
Pathogenesis of ABO haemolytic disease of the newborn?
immune** ABO antibodies (IgG) crossing the placenta to destroy the RBC’s of the foetus
Usually group ‘O’ mothers with non-’O’ foetus
mild & self-limiting
What type of molecule is Rhesus factor?
transmembrane polypeptide with >50 antigenic specificities
List the main Rh antigenic specificities? What genes code for Rh?
D, C, c, E, e
2 closely linked genes: D & CcEe (CE, Ce, cE, ce)
Which Rh factor is most tested for and most common in HK population
Rh (D)
99.7% / all Chinese = Rh(D) positive
How are Rh Ab formed? Type of Ig? Cross placenta?
Warm-reacting IgG
Acquired after exposure to the antigen that the patient lacks
Can cross placenta
Pathogenesis of Rh-caused HDN?
Rh -ve mother and Rh +ve father make Rh +ve fetus
Mother’s immune system forms Anti-Rh IgG when exposed to fetal blood
1st pregnancy not affect, but 2nd preg. with Rh+ve fetus again»_space; severe HDN
Difference between Transfusion reaction due to Rh factor and ABO incompatalibity?
Rh incompatability:
- immune/ IgG** Anti-Rh Ab
- Extravascular haemolysis (like ABO incompatability) in liver, spleen
- NO haemoglobinuria, haemoglobinemia, haemosideruria
- Decrease** in haptoglobin
Which type of antibody incompatibility is insignificant?
Cold antibodies
List the blood bank tests for RBC and plasma?
Plasma:
- Crossmatching
- Antibody screen
- Plasma screen
RBC:
- Cell grouping (antigen present)
- Red cell phenotype
- Direct antiglobulin test (DAT)
Principle of serum Ab screening?
Screen for clinically significant antibodies against non-ABO (e.g. Rh factors, Kidd, Duffy)
i.e. Anti-Rh(D) Ab positive = must not have Rh(D) naturally
Principle of blood agglutination tests?
RBC + anti-serum with known blood group specificity (e.g. with Anti-A, Anti-B antibody)
> > Agglutination = RBC has antigen against Ab specified in the anti-serum
> > No agglutination = RBC does not have the antigen against Ab in anti-serum
Difference in function between Direct and Indirect antiglobulin test?
Direct = detect human Ig (e.g. AutoAb, pathological) already attached to RBC*** with anti-human-immunoglobulin antibody (AHG reagent)
Indirect = Detect RBC antibodies (natural) in serum/ ABO testing with AHG
Describe the steps in Indirect Antiglobulin Test, IAT?
- Incubate serum (i.e., Ab) with RBC’s (i.e., Ag)
- Ab will only coat the RBC’s bearing the Ag
- Add AHG reagent to get agglutination
If the antigenic make-up of the RBC’s is known, the specificity of the Ab can be deduced
Describe how RBC allo-antibodies are acquired? What is the response upon secondary exposure of incompatible blood?
acquired through sensitizing events:
- Pregnancy (especially labor)
- Transfusion
Secondary exposure = Surge of IgG cause extravascular hemolysis»_space; delayed hemolytic transfusion reaction
Compare the course of action if blood bank testing on donor serum and RBC returns positive or negative?
Positive = (~7%) further screen specifically to pick compatible blood
Negative = perform electronic crossmatch to select ABO blood group = give ABO, RhD compatible blood
Which blood type is given urgently to massive blood loss?
Unmatched group O blood (immediate)
Unmatched ABO group specific blood (25mins to test ABO and RhD)
Distinguish the IAT, DAT and Ab specificity results for autoimmune and alloimmune haemolytic anemia?
Autoimmune = Both DAT + IAT positive, Autoantibody with broad specificity
Alloimmune = positive IAT &/or DAT, Alloantibody with defined specificity
List some causes of Warm-antibody type AIHA?
1) Idiopathic
2) asso. with:
Autoimmune diseases
Lymphoproliferative disorders (LPD)
Drugs***
List some causes of Cold-antibody type AIHA?
1) Idiopathic
2) asso. with:
Infections*** (infectious mononucleosis, mycoplasma)
LPD, e.g. lymphoma
3) Paroxysmal cold haemoglobinuria
List 2 alloimmune haemolytic anemia?
Haemolytic transfusion reaction
Haemolytic disease of the newborn
What special blood component is given to severely immunocompromised patients (e.g. after chemo/radi)?
Irradiated blood components: prevent transfusion associated graft versus host disease
3 indications of Leucocyte-depleted Blood Components ?
– Prevention of HLA alloimmunization (long-term transfusion support or potential BMT recipient)
– Prevention of Febrile non-hemolytic transfusion reactions FNHTR (Ab vs donor WBC)
– Prevention of CMV transmission
List 4 acute complications of blood transfusion
- Acute haemolytic transfusion reaction
- Febrile non-haemolytic transfusion rxn (Ab rxn with transfused WBC)
- Urticaria (Ab rxn with transfused proteins)
- Pulmonary edema
Rare:
- Infective shock (contaminated blood)
- Anaphylaxis, Transfusion related acute lung injury
List 4 delayed complications of transfusion?
- Delayed haemolytic transfusion reaction
- Transfusion transmitted infections (viral mostly)
- Iron overload
- Ab develop to transfused WBC/ Plt
List some ways to ensure blood safety?
- Stringent donor selection criteria
- Sensitive virological/microbiological assays
- Comprehensive serological workup
- Proper preparation, QC, storage conditions
Role of doctor in ensuring transfusion safety?
- The right specimen from the right patient
- The right unit for the right patient
Positive Identification of Patient
Informed Consent in Transfusion: risk, benefit, alternatives
Transfuse the minimal amount
3 targets of patient blood management?
- Optimize Hb
- Minimize blood loss
- Rationalize transfusion
Alternatives to red cell transfusion for iron deficiency anaemia?
Iron replacement
– Oral iron: FeSO4, Ferrum Hausman Solution
– IV iron: Venofer, Monofer
Organization of Hospital Transfusion Service (3 parts)
Hospital transfusion commitee: oversees:
1) Hospital Blood Bank
2) Users of all disciplines (Medical & Nursing Staffs)
