Learn about safe blood transfusions, donor selection criteria, mandatory testing (HIV, HBV, HCV), ABO/Rh blood groups, and the Coombs' test. Essential medical g
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 - Transmitted by cells or plasma - Excluded donors: male homosexuals, bisexuals, IV drug users, prostitutes, their sexual partners, partners of haemophiliacs - Sub-Saharan Africa and South-East Asia high-risk - Window period transmission possible (donor incubating infection but antibody-negative) CMV - Usually subclinical but can cause infectious mononucleosis - Dangerous in: premature babies 5–10 x10^9/L (higher if sepsis, drug use, coagulation disorders) - Invasive procedures (liver biopsy, lumbar puncture): raise to 50 x10^9/L - Brain or eye surgery: raise to 100 x10^9/L - Massive haemorrhage: keep 50 x10^9/L (Chapter 26) Avoid platelet transfusion in: - Autoimmune thrombocytopenic purpura (unless serious haemorrhage) - Heparin-induced thrombocytopenia - Thrombotic thrombocytopenic purpura - Haemolytic uraemic syndrome Refractoriness to platelets: - Poor increment post-transfusion: 400 antigens; ABO and Rh most important - Group O or B subjects develop natural IgM antibodies; these may haemolyse or opsonise incompatible donor red cells - Antibodies also develop from transfusion or pregnancy; cross-matching ensures compatibility - Complications: haemolytic reactions, febrile reactions, circulatory overload, infection transmission (especially viral), iron overload - Components other than red cells include: platelets, FFP, albumin, coagulation factor concentrates, immunoglobulin