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Since the UK advent of sustainable large scale blood banking in the 1940s the therapeutic use blood products via transfusion has become an invaluable and life saving treatment with many applications. Each year the National Blood Service (NBS) collects in the region of 2.1 million blood donations which are processed into a variety of therapeutic blood products to supply the National Health Service (NHS) with the 8,000 units of blood it uses on a daily basis. As with any medicine it is crucial to regulate the quality of production and its directed application so that the safety and efficacy of the final product may be ensured, a point which is especially important when considering the origin and natural variability of therapeutic bio-products and their potential to cause a serious hazard of transfusion. Consequently the NBS follows strict guidelines set out in the Red Book for the collection, testing, processing, storage and issue of blood products, and is regulated by the Medicines and Healthcare products Regulatory Agency (MHRA) in accordance with the guidelines for production of therapeutic products detailed in the Orange Book which enforces compliancy with the Red Book and Good Manufacturing Practice (GMP), thus guaranteeing the quality of each unit produced.
Initially prospective donors complete a questionnaire regarding their recent state of health, medical history, medication, travel and lifestyle choices which aims to defer "high risk" donors, who have a greater potential risk of being infected with a blood borne pathogen that could be transmitted via transfusion e.g. HIV, hepatitis C, vCJD etc., either temporarily or permanently depending upon their circumstances. Haemoglobin levels are also measured by needle prick to ensure minimum red cell content in the final product. Once a donor is considered suitable the needle puncture site is disinfected and blood is collected into a sterile pack whereby the first 20-30ml is discarded to prevent contamination by bacterial skin flora.
Table 1. UK mandatory screening tests for blood donations.
ELISA: HBsAg, and NAT on certain types of donation e.g. cord blood.
ELISA: Anti-HCV, and NAT on pooled samples of 48.
ELISA: Anti HIV-1, anti HIV-2 and combined HIV-1 Ag, and NAT: HIV-1 on pooled samples of 48.
ELISA: Anti-HTLV on pooled samples of 48
Antibody detection assays
Forward and reverse serological grouping (repeat donors matched against previous results, first time donors tested twice and matched) and high-titre anti-A and anti-B in blood group O
Rh & K Typing
Forward serological grouping including weak variants
Reverse serological screening for clinically significant high titre red cell Abs against O R1R2 K red cells and HLA typing for some products
As well as the collection of the donation, accessory samples of blood are taken for mandatory screening tests (Table 1) which aim to prevent transfusion transmitted infections (TTI) and provide blood group information. Testing has evolved over time and controversially a number of these tests have come about due to notable TTIs before their advent e.g. numerous haemophiliacs were infected with HIV in the 1980s after transfusion with clotting factors from infected individuals before testing was implemented. Other screening tests which may be undertaken if the situation indicates include: malaria and Chagas' disease e.g. after foreign travel to affected areas, hepatitis B core Antigen (anti-HBc) e.g. after skin piercing, CMV (anti-CMV) screening on approx. 20% of donors to ensure a CMV negative store of components and grouping on approx. 15% donations to provide phenotyped products for rarer groups e.g. Cw, M, S, s, Fya/b, Jka/b, Kpa, Lua etc. Donations that fail to meet testing requirements are immediately flagged and held for discard, whilst the donor is notified and deferred.
Blood and blood products are highly labile and undergo potentially harmful changes that affect transfusion outcome known as storage lesion, whereby red cell and platelet viability degrades; ATP and 2,3-DPG are progressively lost resulting in lipid membrane alteration and loss and increased haemoglobin affinity for oxygen, pH falls dramatically and electrolyte changes are seen. However with correct processing and storage of components most of these changes are reversible within the first 24hrs after transfusion, although older products will obviously show a decreased rate of recovery compared to fresher ones. The initial donation is collected into a sterile pack containing a Citrate-phosphate-dextrose-adenine anticoagulant to prevent clotting and ATP loss. Donations are then kept at room temperature until processing to preserve platelet viability, which degrades at low temperatures. Typically whole blood donations undergo centrifugation to separate the plasma, buffy coat and red cells. Red cells are expressed from the bottom of the pack into a sterile satellite pack under a closed system to prevent contamination and resuspended in an optimal additive solution of saline-adenine-glucose-mannitol (SAGM) to prevent ATP and 2,3-DPG loss, units are then leucodepleted by filtration with the aim of reducing immune related complications e.g. HLA alloimmunisation, and removal of viruses e.g. CMV and prions e.g. vCJD, and may be stored at 2-6°C for 35 days. The plasma is expressed into a satellite pack under closed conditions from the top of the original pack leaving the buffy coat which are both then leucodepleted. Platelet preparations may then be made by pooling 4 buffy coats into a satellite pack under closed conditions which are resuspended in a mixture of plasma and platelet additive solution to reduce platelet storage lesion. Platelets are stored in breathable packs at 20-22°C and gently agitated to reduce the decline of pH and platelet activation and loss, however platelets are highly labile and coupled with the warmer storage conditions have a lesser shelf life of 4-7 days depending on processing, and must be carefully monitored for contamination. Other components including, granulocyte preparations, fresh frozen plasma (FFP), cryoprecipitate and cryosupernatent are also prepared from plasma and buffy coats, however due to the advent of vCJD in the UK FFP is now bought in from the US from male donors in a bid to reduce the risk of infection and immune reactions e.g. TRALI, from alloimmunisation by donations from multiparous women. FFP may undergo further pathogen inactivation after leucodepletion with the addition of methylene blue and exposure to visible light, or by pooling approx 1500 units and treating them with a solvent detergent, units may then be safely stored at -30°C for 24 months. Finally some situations e.g. neonatal exchange transfusions and granulocyte preparation transfusions require gamma irradiation of units to prevent immune reactions e.g. transfusion related-graft versus host disease.
The Serious Hazards Of Transfusion (SHOT) scheme has been collecting haemovigilance data for the UK since 1996 and reports that acute transfusion reactions (18.5%) and bedside errors e.g. incorrect unit transfused (39.6%), Anti-D (10.8%) and handling and storage errors (10.6%) are the most routine cause of adverse transfusion events, therefore it is of the upmost importance that transfusion laboratories and clinical transfusion staff adhere to guidelines at all times. Initially the patient has blood taken for group and screening tests, whereby the phlebotomist must perform checks to ensure the patients ID and record the correct information on the request form and sample bottles. The transfusion laboratory then serologically ABO and RhD groups the patients red cells and 'reverse groups' their plasma for anti-A and anti-B, and in some cases be grouped for K antigens or be fully Rh and K phenotyped. Screening for clinically important "warm" red cell alloantibodies should be undertaken by Indirect Antiglobulin Test (IAT) at 37°C, whereby the patient's plasma is screened against three selected screening cells of group O blood representing combinations of; R1R1, R1wR1, R2R2, K, JKa/b, S, s, Fya/b, and if antibodies detected the patients plasma tested against an identification panel of fully typed red cells. Like the donation the patients group and screen results are either historically matched with existing results or tested twice to avoid error. A cross match may then be undertaken using the selected donations red cells against the patients plasma to ensure compatibility, however this is more routinely performed electronically nowadays as unforeseen incompatibility is low and removes the possibility of technician error. Once blood is matched it is labelled with the patient's details and issued for transfusion whereby two members of staff must positively identify the patient using a wrist band at the bedside or operating theatre as well as matching the compatibility form, unit prescription, patient notes and unit and its expiry to be transfused. It is helpful to note that each step of the transfusion process may now be computerised using barcoded labels in the aim of reducing adverse transfusion incidents and promoting a transparent and traceable safe system. Transfusion must be given in a timely manner to avoid component expiry or transfusion overload and the patient must be carefully monitored by staff trained to recognise and take the correct action to signs of transfusion reactions e.g. fever, chest pain, decrease in blood pressure, rigor, shortness of breath etc. In the advent of a transfusion reaction staff are obliged to report the incident to the SHOT team via the MHRAs Serious Adverse Blood Reactions and Events (SABRE) system so that data may be analysed for future prevention strategy, which in conjunction with transparent and traceable system, clinical audit and governance transfusion safety may continue to evolve.