10 Compatibility Testing

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  • Compatibility testing is a collection of different processing; a series of testing procedure and processes with the ultimate objective of ensuring best possible result of a blood transfusion
  • Strict adherence to and application of each parameters of compatibility is imperative to the management of safe blood transfusion.
  • ABO/Rh is the foundation of compatibility testing.
    • If you’re donor and recipient are not match, there is no sense of continuing compatibility testing
  • Serological crossmatch phases:
    • Immediate spin or saline phase
    • 37°C or Thermophase
    • AHG phase
  • Major Crossmatch is routinely perform in laboratory
    • Patient serum + Donor Red Cell
    • Generalized antibody screening – what antibody is present.
    • We look for antibodies against donor red cell
  • Minor Crossmatch is widely replace by antibody screening
  • Antibody screening or alloantibody identification looks for alloantibody in the patient serum or plasma
    • We can identify antibodies present in the patients serum that could potentially react with your donor red cells
  • Clerical error is the major cause of transfusion associated fatalities (greatest test)
  • Common causes of errors:
    • Misidentification of recipient – pre-analytical error
    • Mix-up of samples during processing – analytical error
    • Misidentification of recipient when transfusion is given – post-analytical error
  • Patient’s wristband ID must always be compared to requisition form
  • Ideally, serum is the preferred sample for blood bank
  • Incompatible crossmatch is indicated by agglutination and that means that there is antibodies against the red cell → can be seen in serum or plasma.
  • Hemolysis is a false positive error
  • Patient with hemolytic anemia is not rejected
  • Samples in BB are usually in red top tube because tubes with clot activators might contaminate the serum and can cause false agglutination.
  • In blood bank, tubes used are:
    • Purple / lavender EDTA - is used in hematology section
    • Pink EDTA – is specific for blood bank
  • Donor sample must be collected at the same time as the full donor unit
  • Donor information/medical history card, pilot samples and collection bag must be labeled with the same unique numbers before starting the phlebotomy
  • RBCs for donor pre-transfusion testing can be prepared from segmented tubing through which donor blood was collected
  • Using a heat sealer, we segment the tube and each segment can be used for testing.
    • Note: donor and recipient samples must be stored for a minimum of 7 days post transfusion (stoppered, labeled 1-6°C) in relation to transfusion reaction
  • Serological testings:
    • DONOR → ABO, Rh, test for blood-borne diseases
    • RECIPIENT’S → ABO, Rh, unexpected clinically significant antibodies
  • Serological crossmatch purpose is for primary test for determining whether the patient has antibodies against donor red cell
    • Patient serum + donor RBC
  • Immediate Spin Phase
    • PSDR + quick centrifugation (20-30 sec)
    • Absence of agglutination or hemolysis indicates compatibility
    • IgM antibodies was detected because of room temperature → False reactions may be seen in other IS reactive antibodies (cold agglutinins)
  • 37°C phase
    • PSDR incubate for 15-30 mins at 37°C
    • centrifuge (no agglutination proceed to next step)
    • Antibody detected is IgG because they react at warm temperatures
  • AHG Phase
    • PSDR + Immediate Spin + 37°C + AHG
    • Enhancement media may be applied
    • LISS, BSA, PEG
    • Absence of agglutination or hemolysis indicates compatibility
    • Need of washing to remove unbound antibodies
  • Donor’s autoimmune condition can cause false positive
  • If the patient has a high gamma globulin or the patient has a multiple myeloma, the results will be false agglutination
  • Antibody screening
    • Recipient’s serum or plasma
    • To detect as many clinically significant unexpected antibodies antibodies as possible (IgG, 37°C AHG)
    • Clinically significant antibodies are reactive at 37° and have cause HTR, HDN
  • Some labs employed shortened incubation time and enhancement medium to accelerate Ag-Ab reaction, which may result in false negative
  • In extreme emergencies, Group O Rh negative PRBC (universal) may be used.
  • Resorting to Rh positive is best made immediately if patient is a man or woman beyond child bearing age
    • Men are not at risk of developing transfusion reaction
  • Administration of RhIg is to prevent anti-D formation after crisis has been resolved
  • Compatibility testing in Plasma product
    • not required– no RBC
    • Donor plasma + recipient’s RBC
    • To detect ABO compatibility