Blood transfusions Flashcards
Describe the ABO system
Red cells have surface antigens which are glycoproteins or glycolipids.
Blood group A- A antigens
Blood group B- B antigens
Blood group AB- A and B antigensa
Blood group O- No antigens
Blood group O: universal DONATORS
Blood group AB: universal RECIPIENTS
Describe the naturally occurring antibodies to ABO antigens
They are IgM (immature, form pentamers to increase affinity to antigen, can’t cross placenta)
Complete- this means they are detectable by incubation of RBCs with antibody in saline at room temperature
They occur naturally due to cross-reactivity with gut bacteria antigens
What are alloantibodies? What might they cause?
When might they be produced?
Antibodies in one individual that react to cells of another individual
They are IgG
Incomplete- detected by special techniques e.g. enzyme treated RBC’s, addition of albumin
Intravascular haemolysis- ABO incompatibility
Extravascular haemolysis- Rh incompatibility
These both occur to the the donors RBC in the recipient
Haemolytic disease of the foetus and newborn because of transplacental passage
AFTER SENSITISATION
If exposed to it by transfusion or fatal cells across the placenta in pregnancy
What effects on the body does intravascular haemolysis cause?
Shock, hypotension, tachycardia
Renal failure, groin pain, haemoglobinuria
Disseminated intravascular coagulation
Death
Describe the process of blood grouping
Suspend washed RBCs with diluted anti-A, anti-B, anti-AB and anti-Rh(D)
Carried out in microtitre plates or gels
More increasingly carried out by automated machines
Agglutination= positive test
Control of RBCs with known antigens on surface carried out simultaneously
How might healthcare workers detect whether a donors blood will be well accepted by a recipient?
Compatibility test
Incubate the two samples at 37 degrees with control
When sending samples, the ABO group is tested as well as the plasma screened for atypical antibodies.
How do these atypical antibodies arise?
Due to sensitisation with foreign RBC antigens caused by previous blood transfusion or pregnancy.
Describe the ‘‘Coombs’’ test
Anti-globulin test
Uses anti-immunoglobulin antibody to agglutinate red cell
DAT
Tells us if RBCs are coated with antibody
It is positive after a transfusion reaction and in HDN
Postive in autoimmune haemolytic anaemia
IAT
The IAT is used in the lab for testing blood group antigens
Tells us if a patient is postive for Rhesus and other blood groups
Prior to transfusion and prenatal
Describe the Rhesus blood system
Rhesus positive cannot develop antibodies - 85% of pop
15% of pop is Rh -ve
They will generate antibodies in a process called Rhesus sensitisation. The antibody present is IgG
Haemolytic disease of the foetus and newborn (HDFN) is caused by transplacental passage of maternal red cell antibodies.
How does this occur?
Symptoms?
How is it prevented and treated?
Rarely due to ABO incompatibility as these antibodies are largely IgM (cannot cross placenta)
Rhesus D sensitisation is main cause, it is the production of anti-D in Rh(D)- negative women or blood transfusion.
Other causes involved other antibodies in Rh system e.g. anti-C, anti-Kell, anti-Duffy and anti-JKa
Symptoms: anaemia, jaundice, kernicterus
Prevention:
1) ABO Rh check at 12 weeks (prenatal)
2) Rh-ve women receive anti-D antibody intramuscularly at 28 and 34 weeks to prevent sensitisation
Treatment:
Feotus may be given transfusion of blood compatible with mother
Maternal anti-D levels may be lowered by plasma exchange
Baby tested at birth and if Rh+ve, mother receives further anti-D until Kleihauer test (foetal cells) becomes negative
If already sensitised, then the foetus requires monitoring via trans-cranial Dopplers and may require intra-uterine transfusions if signs of anaemia
How Haemolytic disease of the foetus and newborn (HDFN) prevented and treated?
Prevention:
1) ABO Rh check at 12 weeks (prenatal)
2) Rh-ve women receive anti-D antibody intramuscularly at 28 and 34 weeks to prevent sensitisation
Treatment:
Feotus may be given transfusion of blood compatible with mother
Maternal anti-D levels may be lowered by plasma exchange
Baby tested at birth and if Rh+ve, mother receives further anti-D until Kleihauer test (foetal cells) becomes negative
If already sensitised, then the foetus requires monitoring via trans-cranial Dopplers and may require intra-uterine transfusions if signs of anaemia
What is found in blood?
Red blood cells
Buffy coat- WBCs, platelets
Plasma- albumin, gamma-globulins, coag factors
Water, electrolytes and additives
How are the components of blood preserved?
RBC’s kept for 35 days at 4 degrees celcius
Pooled platelets kept for 5 days at 22 degrees celcius
Fresh frozen plasma for 12 months at -30 degrees Celsius
Can also isolate fibrinogen (cryoprecipitate)
What information is food on the label of a blood pack?
Compatibility Unique donation number Blood product Blood group Expiry date
What is apheresis?
A process in which a patients blood is passed through an apparatus that separates its constituents
