Blood Transfusions Flashcards
List the components of whole blood
RBCs (packed) = RBCs, trace WBC, platelets, plasma
Platelets = platelets, plasma, some RBC and WBC
Fresh Frozen Plasma = Plasma, with all coagulation factors, complement
Cyroprecipitate = fibrinogen, vWF, Factor VIII, Factor XIII
Gamma globulin (IVIG) = IgG
List indications for transfusion of each component in blood
RBCs = increase O2 carrying capacity of blood
Platelets = treat or prevent bleeding due to thrombocytopenia or dysfunctional platelets
Plasma = treat or prevent bleeding due to multi-factor coagulopathy, severe liver disease
Cyroprecipitate = treat or prevent bleeding due to hypofibrinogenemia, factor XIII deficiency, von Willebrand disease, fibrin glue for surgery
Gamma globulin = immunodeficiency disorders, some autoimmune diseases
Describe the common modifications for cellular products (RBCs and platelets)
Leukoreduction
• Reduce febrile non-hemolytic reactions
• Reduce HLA immunization (important for future transfusions)
• Reduce CMV risk (because virus lives in WBCs)
Irradiation
• Prevent transfusion-associated graft-vs-host disease (in severely immunosuppressed patients)
Define what is meant by a blood group
Blood group = family of related antigens determined by alleles at a gene locus, or a cluster of linked genetic loci
o >20 systems of RBC antigens
Describe the ABO system
Most important
Genetics: locus on chromosome 9
ABO antibodies = IgM (may also be IgA and/or IgG)
• “Cold-reacting” and don’t need extra reagents for agglutination
• Group A = make IgM anti-B
• Group B = make IgM anti-A
• Group O = make both IgG and IgM anti-A and anti-B
Biochemistry:
• A, B, H antigens located on glycosphingolipid molecules = Encoded for by different alleles
• Group O = unaltered H chains
• Group A = adds N-acetyl-galactosamine to H chain → A chain
• Group B = adds galactose to H chain → B chain
Clinical importance
• Most important blood grouping system because of naturally and regularly occurring antibodies
• 1st step in pretransfusion testing = determine ABO group to prevent Ab and antigen reaction = prevents immediate hemolytic transfusion reaction
Describe the Rh system
Rh ab’s are usually IgG
Genetics: located on chromosome 1
• 2 different genes encode for D and for Cc/Ee proteins
• >30 Rh antigens but only routine to test for Rh D antigen
• 85% people = Rh(+); 15% = Rh(-)
Anti-D antibodies
• NOT naturally occurring in Rh-negative people
• Develop only after exposure to Rh antigen (Ex: transfusion or pregnancy)
Clinical importance:
• Rh matching prevents immunization in an Rh(-) person
• Important for child-bearing women:
o Rh(-) women with Rh ab’s may be unable to bear Rh-positive children = die in utero from hemolytic disease of the newborn
Describe the non-ABO RBC antigen systems
(ex: Kell, Duffy, Kidd, MNSs, Lewis, I antigens)
• Ab’s against these minor RBC antigens are very uncommon
• Have weak antigenicity → low risk of immunization
Describe the process of typing and crossmatching red cells for transfusion, and the method used to screen for unexpected red cell antibodies; explain the importance of each step.
Type (direct antibody test)
o Purpose: prevents transfusion of ABO incompatible RBCs and AHTR
o ABO blood type
o D antigen of Rh group
Screen (Indirect Antibody Test)
Does patient have antibodies to non-ABO red cell antigens?
• Mix patient plasma with RBCs from 2-3 type O RBCs (with known phenotype)
• Antibodies are IgG = don’t cause agglutination
• Need anti-human globulin (AHG) to bridge gap
• AHG are directed against Fc part of IgG
• Allows for agglutination
If no agglutination = negative
If agglutination = antibody panel to find antibody specificity (antibody identification)
• Similar to IAT but tests more cells
• Purpose: be able to give antigen-negative RBC units
Crossmatch
o Is patient compatible with this RBC unit?
• Patient plasma + unit RBCs
o Redundant but can capture errors
Indirect Antibody Testing (IAT) vs. Direct Antibody Testing (DAT)
IAT (Screen): Plasma Source: Patient RBC Source: Reference AHG type : Anti-IgG Question answered: Are non-ABO ab’s in patient plasma?
DAT: Plasma Source: Patient RBC Source: Patient AHG type: Polyspecific → monospecific Question answered: Are ab’s on patient RBCs?
Acute Hemolytic Transfusion Reaction (AHTR)
First symptoms: fever, chills
Other symptoms include: hypotension, shock, oliguria/anuria, DIC
Damage = dose-dependent
• Complement activation to C9
• MAC forms = makes holes in RBCs → intravascular hemolysis
• Free hemoglobin in urine and plasma → decreased NO
• Vaso-constriction → acute renal and multi-organ failure
• At greatest risk = kidneys
So important to stop transfusion, give saline and diuretics
• Overall mortality = 10%
Delayed hemolytic transfusion reaction (DHTR)
Timeline:
• Day 0: pre-transfusion Ab screening is negative (Ab titer below detectable levels)
• Day 1: RBC transfusion
• Days 3-10: Clinical signs of hemolysis may appear (due to accelerated destruction of donor RBCs)
• Days 10-21: post-transfusion sample: positive DAT and positive Ab screen due to newly detected Ab (due to increased Ab titer)
• Days greater than 21: DAT may become negative (Ab-sensitized donor RBCs are removed from circulation)
Typically not require treatment
• Main use = identifies Ab specificity and cause of hemolytic anemia
Immediate extravascular hemolysis
o Usually from mismatched Rh, Duffy, Kell, or Kidd system antigens
o Occurs when Ab binds to RBC membrane antigen without completely activating complement
• IgG-coated RBCs phagocytosed by macrophages
o Rarely fatal
o Usually chills and fever; may get jaundice if rapid phagocytosis
Transfusion-associated acute lung injury (TRALI)
o Most common cause of transfusion-related death
• Severe lung injury
• Occurs within hours after transfusion
o Patients usually have underlying condition (ex: sepsis, pneumonia) = Primes neutrophils → release activating substances
o Results in endothelial damage → leakage into pulmonary airspace = edema
Treatment:
• Supportive
• Oxygen and assisted ventilation if needed
Volume-related transfusion reactions
o Hypocalcemia (citrate overload since citrate binds free Ca2+)
o Hyperkalemia (K+ leaked from stored RBC)
o Acidosis (H+ ions in storage solution plus glycolytic products)
o Alterations in oxygen transport (2,3-DPG depleted in stored blood)
o Bleeding (from dilution of clotting factors)
o Respiratory insufficiency (due to volume overload)
o Treat: diuretics
List the major infectious complications of transfusion in order of frequency; describe the precautions taken to prevent these complications.
Infections: CMV: common Hepatitis B: 1/350,000 Hepatitis C: 1/1,200,000 HIV: 1/1,400,000
Other infections: West Nile, Human Herpesvirus 8, HTLV-1&2, toxoplasma, malaria, Chagas disease, syphilis, human form of bovine spongiform encephalopathy
Measures:
o Improved donor screening
o Lower threshold for giving blood for chronic anemia (7-8 g/dl instead of 10 g/dl)
