Blood Transfusion: Governance, Donor Selection & Blood Group

Blood Trans & Governance Blood transfusion = safe transfer of blood components from donor to recipient UK: all blood banks inspected by the Medicines and Healthcare Regulatory Agency (MHRA) Adverse events reported to SABRE scheme Errors reported to SHOT (Serious Hazards of Transfusion) scheme Donors are voluntary; blood is donated into plastic bags with anticoagulant (citrate, phosphate, dextrose — CPD ) --- 2. Blood Donor Selection (Table 30.1) Age 17–70 years (max 65 at first donation) Weight 50 kg Hb 134 g/L men, 120 g/L women Max 3 donations/year; min 16 weeks between donations Apheresis for platelets/plasma: up to 24 times/year Exclusions: Cardiovascular disease, epilepsy, CNS disorders, cancer, diabetes (insulin-dependent), renal disease, IV drug users Occupations where delayed faint is dangerous (pilots, drivers, crane operators) Defer 12 months after tattoo/piercing, paid sex, homosexual sex, acupuncture Defer 12 months if history of hepatitis; accepted if HBV/HCV markers negative Defer if travel suggests infection risk --- 3. Donor Testing (Table 30.2 — England & Wales) 1. Blood group, Rh status (D, C, E, c, e), K antigen 2. Screen for red cell alloantibodies 3. Microbiological tests: HIV 1 & 2 (antibody + RNA) HBV (antibody + RNA) HCV (antibody + RNA) HTLV (antibody) CMV (antibody — for immunosuppressed recipients) Malaria antibody screening (exposed donors) Chagas' disease antibody (exposed donors) Syphilis antibody (all donations) No reliable test for prions currently available --- 4. Red Cell Antigens & Blood Groups Clinical significance: individuals lacking a blood group antigen may produce antibodies against it, causing haemolytic transfusion reactions (~400 red cell antigens described) ABO System Encoded by a single gene with 3 alleles: A, B, O A and B alleles add carbohydrate residues to a basic glycoprotein (H antigen) A adds N-acetyl galactosamine; B adds d-galactose Naturally occurring antibodies (IgM, occasionally IgG) present in plasma of those lacking the antigen — even without prior transfusion Phenotype Genotype Antigens Natural Antibodies UK Frequency ----------- ---------- ---------- -------------------- -------------- O OO O (H) Anti-A, Anti-B 46% A AA or AO A Anti-B 42% B BB or BO B Anti-A 9% AB AB AB None 3% A and B antigens present on most body cells including WBCs and platelets In 80% of population (secretors), antigens also found in saliva, plasma, semen, sweat Rh System Two closely linked genes: RhD and RhCE RhD encodes D antigen (present = Rh+, absent = Rh–) RhCE encodes C/c and E/e antigens via alternative splicing Rh antibodies do NOT occur naturally — result from transfusion or pregnancy Anti-D is clinically most important; also anti-C, anti-E, anti-c, anti-e Anti-d does not exist Most common Rh genotype in UK whites: CDe/cde (Rr) = 31% Other Blood Group Systems (Table 30.3) Kell, Duffy, Kidd, Lewis, MN, P, Lutheran, Li Less clinically important than ABO and Rh Immune antibodies detected infrequently Molecular techniques increasingly used for extended red cell genotyping --- 5. Blood Group Serology Techniques Antiglobulin (Coombs') Test — fundamental test in transfusion Antihuman globulin (AHG) is produced in animals after injection of human globulin When AHG added to red cells coated with immunoglobulin or complement → agglutination = positive Direct Antiglobulin Test (DAT): Detects antibody/complement already on red cells in vivo Positive in: haemolytic disease of newborn, autoimmune haemolytic anaemia, drug-induced haemolysis, haemolytic transfusion reactions Indirect Antiglobulin Test (IAT): Detects antibodies in serum that have coated red cells in vitro Used for: routine antibody screening pre-transfusion, blood group antibodies in pregnancy Compatibility Testing (Table 30.8) Donor cells tested against recipient serum For IgM: saline at 37C For IgG: indirect antiglobulin test at 37C, low ionic strength saline, enzyme-treated red cells Cross-matching Steps 1. ABO and Rh group determined from patient 2. Serum screened for antibodies (IAT on group O red cells panel) 3. If alloantibody found → donor blood selected lacking that antigen 4. Electronic cross-match available if group + antibody screen done twice --- 6. Hazards of Allogeneic Transfusion Infectious Agents (Table 30.7) Viruses: Hepatitis A, B, C, D (D requires co-infection with HBV) HIV 1+2 HTLV I + II CMV, EBV, HHV-8 Parvovirus B19 West Nile virus, TTV, GBV-C Bacteria: Endogenous: Treponema pallidum (syphilis), Borrelia burgdorferi (Lyme), Brucella, Yersinia/Salmonella Exogenous: Staphylococcal spp., Pseudomonas/Serratia Rickettsiae: Rickettsia rickettsii, Coxiella burnettii Bacterial infections most frequently transmitted by platelets stored 3 days Protozoa: Malaria, Chagas' disease, Toxoplasmosis, Babesiosis, Leishmaniasis Prions: nvCJD — plasma for fractionation and fresh frozen plasma for infants obtained from USA; blood components from people with nvCJD are excluded as donors in UK HIV Transmission Trans