Blood groups and blood transfusions Flashcards
How many RBC produced every second?
2-3 million produced and released from the marrow every second
What is the lifespan of a RBC?
120 days
What do RBC have on their surface?
Antigens - several hundred are blood group antigens
What is the ABO system?
The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes.
How are ABO antigens inherited?
In a mendelian pattern (a gene inherited from either parent segregates into gametes at an equal frequency)
- Each group has a 25% chance of production
- A + B are co-dominant
- O is recessive to both
When are ABO antibodies developed?
- First true antibodies developed > 3months
- Mixture of IgM and IgG (active at body temp)
- IgM mainly for group A and B
What are the 4 ABO blood groups?
A, B, AB, O
What does having a blood group A mean?
A: dominant, 40%, has anti-B antibodies
What does having a blood group B mean?
B: dominant, 12%, has anti-A antibodies
What does having a blood group AB mean?
AB: Universal acceptor, 3%, no antibodies
What does having a blood group O mean?
O: Universal donor, 45%, no antigens but has both anti-A and anti-B antibodies
What are ABO antigens made of?
Carbohydrates not proteins
Where is the genetic locus of Rhesus antigens?
- On chromosome 1
- 2 genes
- RHD (coding for RhD)
- RHCE (coding for RhC and RhE
What does rhesus being highly immunogenic mean?
D is a null gene, so no protein therefore anti-d is not possible
D is dominant: DD, Dd
- High proportion of D neg people will form Anti-D if exposed to D positive blood
What is Rh Haemolytic disease
- Mother is Rh-negative with Rh-positive baby (From father)
- Rh-positive baby’s blood cells enter mother’s bloodstream
- Invading Rh-positive cells cause production of Rh antibodies
- Rh antibodies remain in mother’s bloodstream
- Rh antibodies attach the Rh-positive baby’s blood causing Rh disease
What are the consequences for a baby with haemolytic disease?
They will become very anaemic (even fatal)
What is the treatment for haemolytic disease?
anti-D immunoglobulin injections, prevents mother from making her own anti-D immunoglobulins and prevent sensitisation
How can we prevent haemolytic disease?
- Detect the mothers at risk
- Maternal fetal free DNA
- Blood types tested early on in pregnancy
- Anti- D prophylaxis - which means giving anti-D immunoglobulin to prevent a woman producing antibodies against rhesus positive blood cells
How can we screen women for their ABO group and Rh D status?
- Using 2 different reagents (Anti-B/A and Anti-D)
- Screen plasma to check for antibodies that could have been made from previous transfusions
- Separate and save the plasma
What does cross matching mean?
Check compatibility between donor RBCs and recipients serum
What does the Coomb’s test do?
It is an immunology laboratory procedure used to detect the presence of antibodies against circulating red blood cells (RBCs) in the body, which then induce haemolysis.
If the blood has no agglutination, the blood is good for a transfusion
As the AHG reagent causes IgG-coated RBCs to agglutinate
What are some indications for transfusion?
- Hypovolaemia due to blood loss
- Severe anaemia with inadequate oxygenation of tissues
- Anaemia – check B12 deficiency before considering blood transfusion, not indicated for iron deficiency or B12 deficiency
What are some early hazards with blood transfusion?
- ABO incompatibility reaction –can be fatal
- Fluid overload – pulmonary oedema
- Febrile reaction – antigens target donor antigens. Can cause life-threatening respiratory failure
- Bacterial and malarial infection
What are some late hazards with blood transfusion?
- Rhesus D and other antibody sensitisation
- Delayed transfusion reaction
- Viral infection, hepatitis B, C and HIV
- Iron overload resulting in cardiac, hepatic and endocrine damage
Who can donate blood?
17-65 yrs old
Min 50kg body weight
Questionnaire done about health, lifestyle, travel, medical history, medications etc
Who can’t donate blood?
Temporary exclusions - travel/ tattoos/ lifestyle
Permanent exclusion – certain infectious diseases
How is blood separated?
- Blood spun to separate down to packed red cells/ buffy coat and plasma
- Plasma only kept from male donors
- Plasma can be frozen to make FFP
How is the separated blood stored?
- Red cells kept at ambient temperature (4 degrees C) for a short time (35 days) then passed through a leucodepletion filter and resuspended in additive
- Buffy coats pooled with donations of matching ABO and D type and then leucodepleted (leucocytes are removed from donated blood) to make platelets
What is the numerical transfusion threshold?
Haemoglobin <70g/dL or <80g/dL if symptomatic
Transfuse 1 unit and re-check FBC (full blood count)
(Normal Haemoglobin 130-150g/dL)
How are platelets stored from a transfusion?
- Stored at 22oC with continuous agitation (prevents clumping)
- 7 day shelf life if they are monitored for bacterial contamination
When are platelets transfused?
used in thrombocytopaenia (low platelet count), however, not useful if deficiency is due to immune anti-platelet antibody
- Platelets need to be matched but not cross-matched
What is Fresh Frozen Plasma and when is it used?
- From male donors only
- Contains coagulation proteins and clotting factors. Used in massive transfusion, dilutional coagulopathy (impaired coagulation), liver disease and disseminated intravascular coagulation (DIC)
How is Cryoprecipitate made?
Thaw Fresh Frozen Plasma (FFP) to 4 degrees C and skim off fibrinogen rich layer
When is Cryoprecipitate used?
Used n DIC and massive transfusion if there is a lack of fibrinogen required for aggregation and precursor to fibrin in coagulation cascade
How is Intravenous immunoglobulin made and when is it used?
- Made from large pools of donor plasma
- Pooled immunoglobulin, used in immunodeficiency, congenital or acquired and some auto-immune diseases
What are some steps for safe delivery of blood?
- Patient identification
- 2 sample rule
- Hand-written patient details
- blood selected and cross-matched
