Lecture 2 - Blood testing and transfusions

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)

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.

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)

• 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.

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

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.

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

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

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

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

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.