Immunohematology and Transfusion medicine Flashcards
Name the antibody class of most ABO isohemagglutinins.
IgM
Explain the ABO antigen situation in a person of Bombay blood type, and the consequences of a transfusion of non-Bombay blood into such a patient.
They have anti A, B, and H. They would have an immune response.
Define the crossmatch, and explain why it is important. Explain how red cells are destroyed following a mismatched transfusion, and why this may be devastating to the recipient.
Crossmatch: The crossmatch therefore is a lab test in which plasma from the prospective recipient is mixed with red cells from the donor.Why? They must ordinarily be identical at ABO and Rh. Now you must ask: are there nevertheless antibodies in this recipient’s plasma which can react with antigens on this donor’s red blood cells? This question is called the crossmatch, and if the answer is yes, and you give the blood anyway, there will be shortened red cell survival and the recipient may even not survive.If the cells agglutinate during the test, IgM and possibly IgG will be present, causing this. They both activate complement, which will opsonize and lyse the red blood cells
Compare and contrast the techniques of the direct and indirect antiglobulin tests and the questions they are designed to answer.
direct antiglobulin test (DAT) asks, Is there antibody already on these cells I am interested in? You rinse off the cells and add antiglobulin to find out. The direct test detects cells that were coated with antibody in vivo.The indirect antiglobulin test asks, Is there unexpected antibody to red cell antigens in this plasma I am interested in? You take red cells, add the plasma, rinse the cells (we assume they haven’t agglutinated,) and then add antiglobulin. If the cells now agglutinate, there must have been antibody to them in the tested plasma, because antiglobulin alone will not react with red cells. [Memory aid: There’s one more step in an indirect test.]
Define heterophile antibody, and identify a common disease in which one type is increased enough to be useful diagnostically.
These are antibodies to one antigen which bind, fortuitously, to another; a fancy name for cross-reactive antibodies. The best example is the antibody that appears in the serum of a patient with infectious mononucleosis; it is really in response to an antigen of the EBV virus, but it happens to react with sheep red blood cells, giving us a quick and cheap presumptive test (the Monospot) for mono. Another example is the antibody against “cardiolipin” that people with syphilis make; there is a similar phosphodiester group in the bacterium Treponema pallidum and the phospholipids extracted from beef heart.
Tell me all about hemolytic disease of the newborn.
The consequences of severe hemolysis in the newborn: The fetus will be born jaundiced. This can be dangerous: high levels of bilirubin (a breakdown product of hemoglobin) can cross the blood-brain barrier and damage the basal ganglia, resulting in cerebral palsy or, if there is very severe damage, fetal death.The way in which the mother becomes sensitized: The mom can be exposed to baby’s RBCs in the 3rd trimester or at birth, and make antibodies to itThe class of antibody to Rh(D) the mother makes: IgG: the only one that crosses the placenta, right?The consequences of sensitization to subsequent fetuses: But in a subsequent pregnancy with another Rh(D)+ fetus, the mother’s antibodies, formed after the first pregnancy, can cross the placenta and destroy the fetus’ red blood cells. In addition, each subsequent pregnancy with an Rh(D)+ fetus boosts her response.The role of Rh-immune globulin: The disease is preventable if, at the time that the mother delivers her first Rh(D)+ baby, she is given IgG antibody to Rh(D) (Rh-immune globulin), the most familiar brand being Ortho’s RhoGAM®. Apparently, these antibodies combine with the fetal red cells, opsonizing them, and they are destroyed before they get a chance to immunize her.
Explain the situation in which ABO hemolytic disease of the newborn can occur.
Occasional people do make IgG isohemagglutinins. This is especially true of group O people. So A or B fetuses of these women are at some risk of ABO hemolytic disease. Mom is O, baby is AB.
Describe the basic process of donor qualification and blood collection relating specific steps to blood safety.
Volunteer blood donation, without significant monetary incentivesdonor completes a questionnaire and provides multiple answers to questions about current or past illnesses or surgery, travel, vaccination, and high-risk behavior.the individual is urged to call back the phlebotomy site with the onset of any symptoms of viral syndrome or other infection.The abbreviated physical exam (vital signs, general appearance, skin, upper extremities) reaffirms the general health of the donor.Screening tests including Hematocrit (Hct) and, in the case of an apheresis platelet donor, platelet count certify the safety for both the recipient and the donor.Skin preparation for the phlebotomy reduces the risk of bacterial contamination of blood products, production of components.Screening lab tests: Hep C, HIV, West Nile
Identify the basic components derived from blood donation, explain the biological characteristics of each component, and compare the optimal storage environment and storage time for each component.
Whole blood: Whole blood is kept at 4-6oC for 35 days to optimize red cell recovery and survival. Platelet and neutrophil function degenerate by 24-48 hours of storage and clotting factors turn over more slowly but well before the outdate.Packed RBC’s: are also stored at 4-6 C for 35 days or longer (42 days) with addition of special rejuvenating solutions to support ATP levels.Fresh, frozen plasma: is an acellular product which is kept at -18C for one year and contains >80% of all plasma procoagulant and anticoagulant proteins as well as complement factors.Cryoprecipitate is made from fresh plasma frozen quickly at -80C and allowed to sit for 18 hours at 4C.Platelet concentrate: Concentrates are stored at 22-24C for 5-7 days in gas permeable bags. During storage, reasonable platelet function is maintained but concentrates are a poor source of clotting factors.WBC concentrates: No storage is allowed. Granulocytes are kept at room temperature and transfused within 8-12 hours.
Differentiate the specific indication for each of the basic blood components: packed red cells, fresh frozen plasma, and platelets.
Whole blood may be used in massive transfusions when 1 blood volume has been shed and replaced with crystalloid or colloid and packed red cells. This component must be crossmatched (anything with significant numbers of RBCs must be crossmatched) and infused through a microaggregate filter (routine infusion set) over 2-4 hrs or more rapidly with acute blood loss.PRBCs: are transfused for oxygen carrying capacity: For chronic anemia, Hct <21-24; acute blood loss, Hct <25-30. PRBCs must be crossmatched and administered like whole blood.FFP: may be used to treat coagulopathy related to procoagulant deficiency (DIC, liver failure, vitamin K deficiency, etc.). Specific clotting factor deficiencies (VIII, IX, VII) are treated with factor specific concentrates. FFP may support anticoagulants in general, but AT-III and protein C concentrates are available. FFP must be type specific and administered as tolerated over 1-3 hrs but not >4 hrs.Platelets: Indication is for bleeding associated with thrombocytopenia and/or platelet dysfunction. Consider ABO type specific/compatible. Infuse over 30-45 minutes.
Explain the infectious risks of blood transfusion and describe strategies to reduce risks of specific agents.
Donations are lab tested for a variety of infectious diseases. Additionally, questionairres address other diseases like CJD, EBV, family, social, travel history. Donors found positive are deferred. The risks of transfusion for transmission of specific agents are extremely low.
Tell me about febrile, non-hemolytic reactions.
Febrile non-hemolytic transfusion reactions (≥ 1°C rise in temperature from pre-transfusion level) and mild allergic reactions (hives, transient skin rashes) are the most common adverse events (1/200 and 1/400, respectively). After confirming that other types of reactions are not occurring in the patient, treatment with antipyretics (e.g., Tylenol) and antihistamines (e.g., Benadryl) are required before re-instating the infusion.
Tell me about immediate hemolytic reactions.
Immediate hemolytic transfusion reactions as a result of infusing incompatible blood products (usually ABO) present an infrequent (<1/30,000) but severe and possibly life-threatening event. The cause is usually misidentifying or mislabeling samples from the patient or donor. Activation of complement and intravascular hemolysis may lead to shock, acute renal failure and disseminated intravascular coagulation. Vigorous supportive care, diuretics and heparin may be required.
Tell me about delayed hemolytic reactions.
Delayed hemolytic reactions represent the process of alloantibody production (1/2,500 transfusions) and slow destruction of the sensitizing red cells with very few symptoms and signs. Documentation of these alloantibodies should become part of the medical record since their existence may increase the risk of immediate hemolytic transfusion reactions with future transfusions.
Tell me about anaphylactic reactions.
Anaphylactic reactions are fortunately rare (1/150,000 transfusions) and usually occur without identifying the specific reagent. The bronchospasm and/or large airway response is treated with epinephrine, benadryl and steroids.
