Alloantibodies And Reactions

Question 1

What is an alloantibody?

Answer 1

IgG antibody formed in response to pregnancy, transfusion, or transplantation against exposure to a non-ABO/RhD antigen not present on the person’s red blood cells.

Question 2

What increases the likelihood of alloantibody production?

Answer 2

The more blood that is transfused, the more likely an alloantibody is produced to an antigen.

Question 3

What are the two main reasons for alloantibody production?

Answer 3

1. Most patients only have anti-A and/or anti-B antibodies due to natural exposure to A and B antigens. 2. Only ABO group and RhD are matched for, allowing exposure to other antigens.

Question 4

What happens if transfused blood contains unmatched antigens?

Answer 4

The patient will produce complementary alloantibodies which can cause haemolysis: Delayed or acute haemolytic transfusion reaction.

Question 5

What type of haemolysis is more commonly caused by alloantibodies?

Answer 5

More commonly causes extravascular than intravascular haemolysis.

Question 6

What is the risk during pregnancy if the mother has clinically significant alloantibodies?

Answer 6

The mother’s alloantibodies can cross the placenta and cause haemolysis of foetal cells, leading to Delayed Haemolytic Disease of the Foetus/Newborn (HDFN).

Question 7

Why are alloantibodies formed during pregnancy?

Answer 7

Alloantibodies are usually formed because the foetus has a different ABO/RhD blood group.

Question 8

What should be done first in acute transfusion reactions?

Answer 8

Must stop transfusion first then assess cause, as this can be fatal.

Question 9

What are common causes of acute transfusion reactions?

Answer 9

Commonly caused by allergy to foreign plasma proteins in the donor unit (anaphylaxis) or bacterial contamination.

The possibility of incompatible blood transfusion needs to be considered.

Question 10

What are the signs of delayed transfusion reactions?

Answer 10

More likely to cause jaundice, fever, and poor Hb increase due to alloantibody formation.

Question 11

What is Transfusion-related Acute Lung Injury (TRALI)?

Answer 11

Noncardiogenic pulmonary edema associated with the transfusion that occurs within 6 hours of cessation of transfusion.

Transfused blood components trigger activation of neutrophils in lung minivasculature.

Question 12

What symptoms do patients with TRALI commonly present with?

Answer 12

Patients commonly present with hypotension and fever.

Question 13

What is Transfusion-Associated Circulatory Overload (TACO)?

Answer 13

Pulmonary edema development caused by fluid/volume overload due to transfusion.

Much more likely in patients with cardiovascular and pulmonary disease.

Question 14

What does a positive indirect Coombe’s test indicate in pre-transfusion tests?

Answer 14

Agglutination suggests that the patient has clinically significant alloantibodies.

Question 15

What is required for compatibility testing between patient serum and donor blood?

Answer 15

Patient serum must be manually crossmatched with donor blood; electronic tissue matching is insufficient.

Question 16

What is the 72-hour rule in pre-transfusion testing?

Answer 16

If the patient has been transfused or pregnant within the last 3 months, testing must be done within 72 hours of obtaining the serum sample.

This rule applies only to red cell products, not to platelet or plasma transfusions.

Question 17

Who is not suitable to become a blood donor in the UK?

Answer 17

Anyone who has been transfused in the UK since 1980 cannot be a UK donor.

Question 18

What restrictions exist for individuals who have lived in the UK regarding blood donation?

Answer 18

Anyone who has lived in the UK in recent years is banned from donating overseas due to variant CJD cases in the 1990s.

Question 19

What are the indications for red blood cell transfusion?

Answer 19

Restores oxygen-carry capacity in patients with low haemoglobin or blood loss, severe haemolytic anaemia, acute blood loss during surgery, trauma, obstetrics, and symptomatic anaemia of any cause (e.g., thalassemia or haemophilia).

Question 20

How can red cell production be increased?

Answer 20

1. Transfusing erythropoietin (EPO) can raise Hb count in patients with chronic renal failure and SLE. 2. Transfusing anabolic steroids such as danazol can increase Hb and haematocrit levels. 3. Administering extra haematinics: B12, folate, iron (oral or V).

Question 21

What are the indications for platelet transfusion?

Answer 21

Only when unavoidable, such as in thrombocytopenia or platelet function disorder causing severe bleeding or high risk.

Question 22

What treatment is given for immune thrombocytopenia (ITP)?

Answer 22

Patient receives immunoglobulin or steroid transfusion and tranexamic acid to reduce bleeding.

Question 23

What should patients with low platelet counts avoid?

Answer 23

Patients should be careful to not use NSAIDs or aspirin as they can impair the function of platelets.

Question 24

What are the indications for using Prothrombin Complex Concentrate (PCC)?

Answer 24

Indications for PCC include:
- Patients with coagulopathy who are actively bleeding or at risk
- Planned surgery or invasive procedure in the presence of abnormal coagulation tests

PCC can be safely administered in patients with cardiac or renal impairment who may be unable to tolerate large volumes of plasma, and doesn’t have to be thawed first.

Question 25

What factors are included in 3-factor and 4-factor Prothrombin Complex Concentrates?

Answer 25

3-factor PCC includes factors II, IX, and X. 4-factor PCC includes factors II, VII, IX, and X.

Question 26

When is PCC used in relation to anticoagulation?

Answer 26

PCC is used for reversing effects of warfarin and other vitamin K antagonist anti-coagulants.

Question 27

Why is PCC preferred over FFP in emergency surgeries?

Answer 27

PCC has much higher amounts of clotting factors than FFP.

Question 28

What are the indications for cryoprecipitate?

Answer 28

Indications for cryoprecipitate include:
- Acquired fibrinogen deficiency
- Significant hypofibrinogenemia or dysfibrinogenemia due to critical bleeding, an invasive procedure, trauma, or DIC

Cryoprecipitate must be transfused within 6 hours of thawing or 4 hours of pooling.

Question 29

What conditions warrant the use of cryoprecipitate?

Answer 29

Cryoprecipitate is used for ongoing low fibrinogen levels after transfusion or where fibrinogen levels are dropping rapidly.