LECTURE 9 (Immunologic blood transfusion reactions)

Question 1

What are the 5 types of Immunologic blood transfusion reactions?

Answer 1

• Allergic/Anaphylactic reaction
• Acute haemolytic transfusion reaction
• Febrile non-haemolytic transfusion reaction
• Transfusion-related acute lung injury
• Delayed haemolytic transfusion reaction

Question 2

Describe the allergic/anaphylactic reaction

Answer 2

A reaction that happens almost immediately (within minutes to 2-3 hrs) due to the release of preformed inflammatory mediators in degranulating mast cells (IgE antibodies)

PATHOGENESIS:
- Type I hypersensitivity reaction against plasma proteins in transfused blood
- IgA-deficient individuals should receive blood products without IgA

SYMPTOMS:
- Allergies: Urticaria, Pruritus (itching)
- Anaphylaxis: Wheezing, Hypotension, Respiratory arrest, Shock

Question 3

Describe the acute haemolytic transfusion reaction

Answer 3

A reaction that occurs during transfusion or within 24 hours due to preformed antibodies (IgG or IgM antibodies)
[patients need to have exposed to antigen ALREADY for a reaction to occur since antibodies are formed in the first exposure]

PATHOGENESIS:
- Type II hypersensitivity reaction
- Typically causes intravascular haemolysis due to ABO blood group incompatibility

SYMPTOMS:
- Fever
- Hypotension
- Tachypnea (abnormally rapid breathing)
- Tachycardia
- Flank pain
- Hemoglobinuria (intravascular)
[Fc portion of antibody attach onto RBC antigen -> Complement is activated -> Lysis of RBC -> blood will be delivered to kidney -> kidney will filter blood into urine]
- Jaundice (extravascular)
[Opsonised RBC will reach macrophages in spleen -> macrophages will phagocytose haemoglobin into unconjugated bilirubin -> will deposit in skin etc and cause JAUNDICE]

[LIFE-THREATENING + CAUSED BY PRE-FORMED ANTIBODIES]

Question 4

Describe the febrile non-haemolytic transfusion reaction

Answer 4

A reaction that occurs within 1-6 hours due to preformed cytokines

PATHOGENESIS:
- Cytokines created by donor WBCs accumulate during storage of blood products
- Reactions are prevented by LEUKOREDUCTION of blood products

SYMPTOMS:
- Fever
- Headaches
- Chills
- Flushing
- MORE COMMON IN CHILDREN

Treatment:
NOT life-threatening, just uncomfortable
- If uncomfortable, stop and give ibuprofen and give again in 1hr

Question 5

Describe delayed haemolytic transfusion reaction

Answer 5

A reaction that occurs over 24 hours but usually presents within 1-2 weeks due to slow destruction by reticuloendothelial system

PATHOGENESIS:
- Anamnestic (rapid production of antibody on second encounter with same antigen) response to a foreign antigen on donor RBCs (Rh[D] or other minor blood group antigens) previously encountered by recipient
- Typically causes extravascular hemolysis

SYMPTOMS:
- Generally self-limited + clinically silent
- Mild fever
- Hyperbilirubinemia (can cause Jaundice)

[CAUSED BY PRE-FORMED ANTIBODIES]

Question 6

Describe Transfusion-related acute lung injury

Answer 6

A reaction that occurs within minutes to 6 hours

PATHOGENESIS:
- Neutrophils are located in the lungs due to recipient risk factors
- Neutrophils are activated by a product (e.g anti-leukocyte antibodies) in the transfused blood + release inflammatory mediators -> increased capillary permeability -> interstitial fluid is pushed out of the capillaries -> pulmonary oedema

SYMPTOMS:
- Respiratory distress
[pulmonary oedema -> harder for alveoli to obtain oxygen -> dyspnea]
- Noncardiogenic pulmonary oedema