Lecture 2 - Blood testing and transfusions Flashcards
Describe/explain ABO blood typing.
ABO blood grouping
The blood type describes the antigens present on an individual’s RBCs, Type A blood has A antigens etc. type O blood has neither A or B antigens.
The body naturally produces antibodies against non-self-antigens. Therefore Type A individuals will have Anti-B antibody in their plasma whilst type O blood has both anti-A and anti-B antibodies.
The antigens on an individual’s blood cells and antibodies within their plasma determines which blood types an individual can receive.
E.g. Type A - Type a has anti-B antibodies so can therefore not receive transfusions from individuals with type B antigens on their RBCs. Therefore they are compatible with Type A and O blood.
Type AB = Universal recipient (as has no antibodies)
Type O = Universal donor (as has both A and B antibodies)
What is the Rh blood group
Rh blood group
The Rh blood group is determined by two genes on chromosome 1 - RHD and RHCE (encode the Rh antigens)
* If the RHD gene is present then the individual is Rh +ve, if the gene is deleted they are Rh -ve.
Alternative splicing gives rise to C, c, E or e antigens.
What methods are used for blood typing.
The old method of blood typing mixed washed (to remove any of the plasma antibodies) RBCs with antibodies against A, B and D antigens. If the corresponding antigen is present on the RBC, the antibody will bind and the RBCs will clump together (agglutinate).
The modern method uses gel based technology where washed RBCs are added to a microcolumn containing gel containing antibodies. It is then centrifuged.
* If the cells agglutinate they stay on the top of the gel (positive reaction)
* If the cells don’t agglutinate they pass through the gel (negative)
Some other tests include:
* Patients serum tested for antibodies
* Crossmatching (patient serum mixed with donor RBCs)
Explain the development of immune antibodies to RhD
- ABO blood groups have naturally occurring antibodies against other ABO antigens
- This is not the case for RhD - anti RhD antibodies can develop by exposure of an RhD -ve recipient to RhD+ donor blood.
*If than RhD- individual receives a second transfusion of RhD+ blood it would cause an immune response which is potentially fatal.
What is haemolytic disease of the newborn
HDN also known as RhD incompatibility occurs when there is an incompatibility between the mother and foetus’ RhD status.
An RhD- mother carrying her firs Rh+ foetus will be exposed to Rh antigens from the developing foetus during delivery and in response the mothers body will produce anti-Rh antibodies. If the women becomes pregnant with another Rh+ foetus her anti-Rh antibodies will cross the placenta and damage the foetus’ RBCs.
This results in fetal anaemia and/or death.
HDN can lead to an accumulation of bilirubin due to increased haemolysis. In utero this is secreted into the maternal blood where it is conjugated in the maternal liver and excreted.
After the birth there is still haemolysis which is problematic for the newborn baby with immature liver and can lead to jaundice
150/100000 births resulted in HDN death until the 1960s
How is haemolytic disease of the newborn prevented?
If the mother is RhD- and the baby is RhD+ the mother is injected with anti-RhD antibodies within 72 hours of birth. The antibody removes foetal RhD+ red blood cells from the maternal circulation meaning that the mother does not make anti-RhD antibodies. Therefore in a subsequent pregnancy an RhD+ foetus will not have their RhD+ RBC destroyed via anti Rh D antibodies.
What might make an individual unable to donate blood in the UK?
Donors in the UK are healthy unpaid volunteers.
Exclude patients with:
* Chronic disease: Cardiovascular; respiratory; renal; CNS; gastrointestinal
* Previous blood transfusions in the UK (risk factor for NV Creutzfeldt-Jakob Disease (nvCJD)
* Pregnant or current infection
* IV drug use and others…
Defer 4 months after last body piercing, tattoo, acupuncture
Defer 3 months after last sexual encounter for sex workers and men who have sex with men
Defer 4-8 weeks after live vaccination
Defer based on travel history if risk of infection
Why is component blood used in modern blood transfusions?
Whole blood transfusions were first attempted in the 1600 and were the norm until 1970s, after which component blood was used almost exclusively.
* Reduce waste as only necessary components of blood used
* Improve storage time
Tailor treatment
Describe blood product preparation (component manufacturing).
Aseptic donation into bag containing anticoagulant (CPD – Citrate, Phosphate, Dextrose)
Citrate binds calcium = anticoagulant
Dextrose – RBCs stay metabolically active
Centrifugation to produce blood components: red cells, buffy coat, plasma
Leucodepletion - Filter blood just after collection to remove majority of white blood cells
* Prevents immune reaction against donor WBCs and febrile reactions
* Helps prevent transmission of CMV and nvCJD
Microbiological testing of donor blood
There are a number of mandatory tests screening for infectious agents for each donation
* HIV
* Hepatitis
* Human T-cell lymphotropic virus (increased risk of developing leukaemia)
* Syphilis
Some donations will require additional tests in special circumstances.
NB – currently there is no reliable test for prions (e.g. vCJD) in blood products
What blood products are derived from donation
Blood products include
* Packed red cells
* Fresh Frozen Plasma (FFP) and cryoprecipitate
* Platelets
The products are barcoded so they can be traced to the donor and records are stored for 30 years to provide a vein-vein trail
What are the uses of each product derived from a blood transfusion
Plasma-depleted red cells (packed cells)
The RBCs are stored at 4-6C for up to 35 days. The transfusion must be completed within 4 hours. It is used to replace blood loss and to correct anaemia. It is irradiated to kill WBCs not removed during leucodepletion
Fresh frozen plasma
FFP is mainly used for replacement of coagulation factors for example, factor VIII in haemophilia
Cryoprecipitate
Made from FFP by thawing slowly at 4C. The precipitate is rich in fibrinogen and Von Willebrand Factor as well as Factor VIII.
Platelets
Platelets are used in thrombocytopenia (low platelet count), platelet function problems, bleeding ro risk of bleeding. They are stored at room temp.
