• When an allo-antibody is detected, its specificity and clinical significance should be assessed.
  • If a patient is known to have formed an allo-antibody, each new sample should be fully tested to include or exclude the presence of other, different allo-antibodies. 
  • The patient’s plasma should be tested against a panel of red cells, and should always include an IAT.
  • Cells in the antibody screen can be used to contribute towards assigning antibody specificity and exclusion of other antibodies.
  • A check should be done to ensure that ABID results do not conflict with screening results (this may reflect the wrong sample being used, or an antibody directed against a low-frequency antigen absent on either panel).
  • Inclusion of the patient’s own red cells as an auto-control may be helpful, but does not exclude the presence of an allo-antibody.
  • Antibody specificity requires that the patient’s plasma react against at least 2 (ideally 3) red cells homozygous for the antigen and does not react against at least 2 (ideally 3) samples negative for the antigen. 
  • Other clinically-significant antibodies must be excluded after the antibody has been identified.
  • Confirmation technically requires that the laboratory demonstrate that the patient is negative for the antigen against which the allo-antibody is directed.
    • The patient’s red cells should be phenotyped using a reagent of the same specificity of the antibody assigned.
    • This must be done with suitable positive and negative controls.
    • If the test against patient’s cells is positive, consider:
      • The antibody may be an auto-antibody.
      • The patient may have been transfused recently with antigen-positive cells.
      • The patient’s cells may be coated with immunoglobulin or complement.
      • The antibody may have been wrongly identified.
      • The wrong sample may have been tested.
    • If the patient has been recently transfused, then phenotyping may be inaccurate due to antigen positivity of the transfused cells; in this case, genotyping can be considered.
  • Panel cells should comprise reagent red cells from at least eight group O donors.
    • For each of the clinically-significant antibodies, at least two cells must be positive and two cells negative for those antigens.
    • The panel should support resolution of as many common antibody mixtures as possible.
  • Panel cells must comprise at least:
    • One R1R1 cell (CDe/CDe)
    • One R1wR1 cell (CDe/CwDe)
      • These should express the antigens K, k, Fya, Fyb, Jka, Jkb, S and s between them.
    • One R2R2 cell (CdE/CdE)
    • One r’r cell (Cde/cde)
    • One r”r  cell (cdE/cde)
    • Thre rr cells (cde/cde)
    • At least one cell must be K+
    • Collectively, at least one cell must be homozygous for  k, Fya, Fyb, Jka, Jkb, S and s.
  • Limitations:
    • Panels may not be able to definitively identify combinations of common allo-antibodies.
    • Use of two panel cells increases the probability of being able to identify multiple allo-antibodies.
  • At least one panel of enzyme-treated cells should be available, as it increases the chance of identifying an antibody mixture where at least one of the antibodies is directed against antigens affected by enzymes.
  • If donor red cells give a positive IAT crossmatch reaction, but the antibody screen/identification is negative:
    • Recipient plasma contains an allo-antibody against a low-frequency antigen which the donor is positive for.
    • Red cells in the donation are coated with IgG.
    • The wrong blood has been selected for cross-matching.
  • If all panel cells are positive but auto-control and DAT persistently negative:
    • If blood group O: consider Bombay blood group.
    • If non-O: consider presence of anti-HI
      • anti-HI can be excluded by testing patient plasma against 

Common Red Cell Antibodies and Their Clinical Significance

SystemAntibody SpecificityClinically Significant?Selection of RBCs for Transfusion
ABOAnti-A1NoIAT XM compatible at 37°C
RhAnti-D, -C, -c, -E, -eYesAntigen negative
RhAnti-CwNoIAT XM compatible at 37°C
KellAnti-K, -kYesAntigen negative
KellAnti-KpaNoIAT XM compatible at 37°C
KiddAnti-Jka, -JkbYesAntigen negative
MNSAnti-M
(active at 37°C)
YesAntigen negative
MNSAnti-M
(inactive at 37°C)
NoIAT XM compatible at 37°C
MNSAnti-NNoIAT XM compatible at 37°C
MNSAnti-S, -s, -UYesAntigen negative
DuffyAnti-Fya, FybYesAntigen negative
PAnti-P1NoIAT XM compatible at 37°C
LewisAnti-Lea, Leb, Lea+bNoIAT XM compatible at 37°C
LuAnti-LuaNoIAT XM compatible at 37°C
DiegoAnti-Wra (-Di3)YesIAT XM compatible
HAnti-HI (in A1 and
A1B patients)
NoIAT XM compatible at 37°C
AllOthers active by
IAT at 37°C
YesGet advice from Blood Centre
Likely clinical significance of red cell antibodies and recommendation for blood product selection in their presence.

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