Alloantibodies And Reactions Flashcards
What is an alloantibody?
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.
What increases the likelihood of alloantibody production?
The more blood that is transfused, the more likely an alloantibody is produced to an antigen.
What are the two main reasons for alloantibody production?
- 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.
What happens if transfused blood contains unmatched antigens?
The patient will produce complementary alloantibodies which can cause haemolysis: Delayed or acute haemolytic transfusion reaction.
What type of haemolysis is more commonly caused by alloantibodies?
More commonly causes extravascular than intravascular haemolysis.
What is the risk during pregnancy if the mother has clinically significant alloantibodies?
The mother’s alloantibodies can cross the placenta and cause haemolysis of foetal cells, leading to Delayed Haemolytic Disease of the Foetus/Newborn (HDFN).
Why are alloantibodies formed during pregnancy?
Alloantibodies are usually formed because the foetus has a different ABO/RhD blood group.
What should be done first in acute transfusion reactions?
Must stop transfusion first then assess cause, as this can be fatal.
What are common causes of acute transfusion reactions?
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.
What are the signs of delayed transfusion reactions?
More likely to cause jaundice, fever, and poor Hb increase due to alloantibody formation.
What is Transfusion-related Acute Lung Injury (TRALI)?
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.
What symptoms do patients with TRALI commonly present with?
Patients commonly present with hypotension and fever.
What is Transfusion-Associated Circulatory Overload (TACO)?
Pulmonary edema development caused by fluid/volume overload due to transfusion.
Much more likely in patients with cardiovascular and pulmonary disease.
What does a positive indirect Coombe’s test indicate in pre-transfusion tests?
Agglutination suggests that the patient has clinically significant alloantibodies.
What is required for compatibility testing between patient serum and donor blood?
Patient serum must be manually crossmatched with donor blood; electronic tissue matching is insufficient.
What is the 72-hour rule in pre-transfusion testing?
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.
Who is not suitable to become a blood donor in the UK?
Anyone who has been transfused in the UK since 1980 cannot be a UK donor.
What restrictions exist for individuals who have lived in the UK regarding blood donation?
Anyone who has lived in the UK in recent years is banned from donating overseas due to variant CJD cases in the 1990s.
What are the indications for red blood cell transfusion?
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).
How can red cell production be increased?
- 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).
What are the indications for platelet transfusion?
Only when unavoidable, such as in thrombocytopenia or platelet function disorder causing severe bleeding or high risk.
What treatment is given for immune thrombocytopenia (ITP)?
Patient receives immunoglobulin or steroid transfusion and tranexamic acid to reduce bleeding.
What should patients with low platelet counts avoid?
Patients should be careful to not use NSAIDs or aspirin as they can impair the function of platelets.
What are the indications for using Prothrombin Complex Concentrate (PCC)?
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.
What factors are included in 3-factor and 4-factor Prothrombin Complex Concentrates?
3-factor PCC includes factors II, IX, and X. 4-factor PCC includes factors II, VII, IX, and X.
When is PCC used in relation to anticoagulation?
PCC is used for reversing effects of warfarin and other vitamin K antagonist anti-coagulants.
Why is PCC preferred over FFP in emergency surgeries?
PCC has much higher amounts of clotting factors than FFP.
What are the indications for cryoprecipitate?
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.
What conditions warrant the use of cryoprecipitate?
Cryoprecipitate is used for ongoing low fibrinogen levels after transfusion or where fibrinogen levels are dropping rapidly.
