L26 – Transfusion beyond Immunohaematology Flashcards by Benjamin Chan

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

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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

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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

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What type of Ig is natural Anti-A, Anti-B antibodies? Can it cross placenta?

IgM

active at body temperature
Cannot cross placenta

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How does Anti-A, Anti-B Ab cause hemolysis of incompatible RBCs?

Anti-A/B IgM can activate complements at body temp&raquo_space; acute intravascular hemolysis

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Difference between natural and immune-induced Anti-A/ Anti-B Antigen?

Natural = IgM

Immune origin = IgG

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Inheritance pattern of ABO gene?

Autosomal dominant

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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

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Define the A,B antigen and Anti-A, Anti-B antibodies in Group A blood?

Have A antigen

Have Anti-B Ab

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Define the A,B antigen and Anti-A, Anti-B antibodies in Group B blood?

Have B antigen

Have Anti-A Ab

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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

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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

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List 2 conditions due to ABO incompatibility

Acute haemolytic transfusion reaction

ABO haemolytic disease of the newborn (HDN)

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Pathogenesis of acute hemolytic transfusion reaction?

Natural Anti-A/B Ab bind to incompatible RBC

Activate complements&raquo_space; acute intravascular haemolysis

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Symptoms of acute hemolytic transfusion reaction?

 Fever

 Hemoglobinemia (free Hb)
 Hemoglobinuria (should differentiate from hematuria by urine microscopy)
 Hemosiderinuria

 DIC = multiorgan failure

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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

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What type of molecule is Rhesus factor?

transmembrane polypeptide with >50 antigenic specificities

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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&raquo_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: 1. Pregnancy (especially labor) 2. Transfusion Secondary exposure = Surge of IgG cause extravascular hemolysis >> 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)