Pretransfusion Compatibility Testing
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| What is in a crossmatch order? | ABO, Rh typing and antibody screen.
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| When is weak D testing not necessary? | For transfusion patients who type as Rh negative. Use Rh neg donor for transfusion.
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| What is the purpose of an antibody screen? | To rule out any unexpected antibodies to blood groups other than ABO.
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| What type of cells are tested in a panel. | O neg cells.
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| What is the Rule of Three? | If plasma reacts with 3 antigen positive cells and does not react with 3 antigen negative cells, there is a 95% probability the identification did not happen by chance.
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| Formula for calculating number of units to be screened: | N = # units needed / negative frequency of antigens
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| Time of specimen if patient was transfused or pregnant in last 3 months | Specimen must be <3 days old
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| What is an autologous donation? | Unit donated by self.
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| What is a directed donation? | Unit donated for a patient by a relative or friend.
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| What is the order of transfusion? | Autologous, directed, then random
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| Antibody screen is negative | Proceed with Immediate spin or electronic crossmatch
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| Antibody screen is positive | Set up antibody panels
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| When is reverse ABO typing not performed? | neonates
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| What is the AABB requirement for all antibody screen? | 37C incubation and AHG phase
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| What is the purpose of add check cells? | To make sure AHG reagent was added.
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| Advantages of Gel Method | Stable for 24 hours; can read at a later time; results more objective; automation
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| How to resolve Rouleaux in gel system? | Use tube AHG method. Saline replacement technique for 37C phase.
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| In solid phase, what is a positive reaction? | Diffuse pattern in well.
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| In solid phase, what is a negative reaction? | Pellet in bottom of well.
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| What should be done after a antibody screen? | Type the patient for the antigen in question. It should be negative for that antigen.
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| What is the universal donor type? | O cells
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| What are compatible pack cells for patient type A? | A, O
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| What are compatible pack cells for patient type B? | B, O
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| What are compatible pack cells for patient type AB? | AB, A, B, O. AB type is universal recipient.
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| what does crossmatch refer to? | Incubation of patient's plasma with donor cells.
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| Immediate spin crossmatch | 2 drops of patient's plasma + 1 drop of donor 2-5% cells, centrifuged immediately, and read for hemolysis and agglutination. Neg reaction indicates compatibility.
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| What is the purpose of IS crossmatch? | final check of ABO compatibility between donor RBC and patient's plasma
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| What are the advantages of IS crossmatch? | Saving time for crossmatch procedure. Fewer units are needed for advance crossmatching, esp. for surgeries.
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| What are the disadvantages of IS crossmatch? | Positive reactions are seen in presence of other non-ABO RT reactive antibodies or rouleaux.
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| Name 3 ways to resolve incompatibilities in the crossmatch? | 1) resolve pos result by ruling out ABO incompatibility
2) perform RT panel to ID presence of cold reactive antibody
3) Resolve rouleaux by repeating IS crossmatch with saline replacement technique.
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| AHG crossmatch | Patient plasma is mixed with donor cells as in IS crossmatch, potentiator is added, incubated at 37C and preform AHG test.
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| If positive incompatible crossmatch AHG | perform DAT on donor RBC. If pos, that donor's RBSs are already coated with IgG and/or complement. Remove DAT-pos donor RBC from inventory.
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| If patient's antibody screen is neg and only one donor unit is incompatible | suspect presence of antibody to low-incidence antigen on donor RBC
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