Blood transfusions Flashcards
ABO blood type
Grouping is based on the antigens present on the rbc and antibodies present in the plasma.
A= A antigen, B antibodies B= B antigen, A antibodies. AB= A and B antigens, no antibodies. O= No antigens, A+B antibodies.
Blood type A
Blood type that contains:
Type A antigens
Type B antibodies.
Can only receive blood from blood types A and O.
Can only give to AB and A.
It is the second most common blood type in the Uk- 42%
Blood type B
Blood type that contains:
Type B antigens
Type A antibodies
Can only receive blood from blood types B and O.
Can only give blood to AB and B.
Frequency of people with type B blood= 9%
Blood type AB
Blood type that contains:
Type A and B antigens
No antibodies
Can receive blood from all blood types.
Can only give blood to AB.
It is the rarest blood type in the UK= 3%
Blood type O
Blood type that contains:
No antigens.
Type A and B antibodies.
Can only receive blood from blood type O.
Can give blood to any blood type - universal donor.
It is the most common blood type in the Uk- 46%
Agglutinins
The antibodies naturally occurring in plasma.
That occur as pentameric IgM antibodies.
These antibodies naturally occur to ABO antigens which are present in gut bacteria.
Cross matching blood types
A method of determining blood groups:
Forward grouping-
Blood group is compared with antibodies
Reverse grouping:
Comparing blood group with rbcs- its antigens.
Rhesus system
Rh receptor is present on red blood cells, coded by Ip36-p22.1 gene.
If an individual is positive for this receptors, they do not create antibodies against Rh antigens.
Around 15% of individuals are Rh-.
Rhesus system and pregnancy
If a pregnant woman is Rh- whilst their baby is Rh+, the mother can develop antibodies that attack the fetus’s cells.
This causes haemolytic disease of the newborn.
This is combated by given the mother Anti-D antibody injections at weeks 28 and 34 to prevent HDN.
Atypical antibodies
These antibodies arise due to sensitisation of foreign rbc antigens.
This is due to pregnancy or previous blood transfusions.
This can cause blood transfusion reactions if the patient is transfused with incompatible blood in the future.
Coombs test
Antiglobulin test
An anti-immunoglobulin antibody is given to agglutinate rbcs
Two types: Direct and indirect
Direct coombs test
This tells us if the rbcs are coated with antibodies- antigens are complementary to antibodies.
- Blood sample is taken from a patient.
- Patient’s washed RBCs are inoculated with Coomb’s reagent (human antibodies).
- If the test is positive, the RBCs will agglutinate, as the human antibodies will form links between them.
This test is positive when:
An individual just had a blood transfusion.
Autoimmune haemolytic anaemia
Haemolytic newborn disease.
Indirect Coombs test
- A recipient’s serum containing antibodies is obtained.
- A donor’s blood sample is added to the serum.
- When positive, recipient;s antibodies will target rbc’s and form antigen-antibody complexes.
- Coombs reagent is added to the solution. This triggers agglutination of red blood cells.
Haemolytic disease of the newborn.
Occurs when the mother is Rh- whilst their fetus is Rh+.
This can lead to the mother’s antibodies attacking the fetus causing:
Anaemia
Jaundice
Kernicterus
Prevention of HDN
Pregnant women are screened for ABO and Rh-D blood group at 12 weeks.
If the mother is Rh-, she receives anti-D antibody intramuscular (i.m) injections at weeks 28 and 34.
Baby is also tested at birth if they are Rh+ whilst mother receives further anti-D.
Mothers receive anti-D until Kleihauer test becomes negative.
