Transfusion medicine

Contributed by Aditi Goel, M.D. and Richa Gupta, M.D.


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• Antibody identification
  • Performed after positive antibody screen (Asian J Transfus Sci 2019;13:34)
  • Principle: serum or plasma is tested against an extended panel of 11, 15, 16 or 20 reagent red cells of known antigen profile (lot specific)
    • Panel should be diverse to include variable expression of clinically significant antigens
    • Profile sheet specifying the different antigens present on the cells or antigram is provided with the panel (see Diagrams / tables)
  • Methodology: basic methodology is the same as antibody screen (see Diagrams / tables), the only difference being the number of cell suspensions used in the panel (2 - 3 in screen versus 11 - 20 in identification)
• Interpreting the antigram
  • Results with all panel cells are recorded on the antigram and the antibody is identified using the following steps
    • Ruling out / exclusion: cells with a negative reaction to all tested phases are used to rule out the presence of antigens
      • Respective antigens on these sets of cells can be eliminated as a possible cause of antibody reactions; cells that are heterozygous should not be crossed to avoid excluding a weak antibody reaction
    • Matching the pattern: the next step is to look at the reactions that are positive and match the pattern; in case of a single antibody, all cells possessing that antigen will show a positive reaction
    • Rule of 3: presence of at least 3 antigen positive red cells that produce a reaction and 3 antigen negative red cells that do not produce a reaction will result in accurate identification of the antibody (p value < 0.05)
    • Strength and phase of reaction: identifying the phase at which reaction occurs (immediate spin [IS] versus 37 °C or AHG) and strength of reaction also helps in identifying the antibody; presence of different reaction strengths with different cells may be due to presence of more than one antibody or dosage phenomenon (stronger reaction with antigen homozygous cells as compared to heterozygous cells)
• Additional tests: required when the identification panel does not yield specific results
  • Selected cell panels: additional panels with different antigen combinations as needed for further characterization
  • Enzymes: RBCs are treated with enzymes like ficin, papain, bromelain to alter the expression of antigens (some enhanced while others inactivated); comparing reactions of treated versus untreated cells with serum can help pinpoint the alloantibody
  • Neutralization: certain substances will result in binding and inactivation of the antibody in the test serum (e.g., saliva for anti-Lewis, hydatid cyst fluid for anti-P1); a positive reaction before neutralization and a negative reaction with the same test cells postneutralization will clearly indicate the presence of specific antibody that was neutralized
  • Use of dithiothreitol (DTT)
    • DTT breaks the disulfide bonds in IgM antibodies and inactivates them, thus helping in identifying the presence of any IgG alloantibody
    • It also breaks the CD38 disulfide bonds on the red cells thus preventing daratumumab from binding to red cells; so it helps in identifying alloantibodies in patients being treated with daratumumab

A 58 year old man presents to the hospital for knee replacement surgery. The patient has a history of blood transfusion a few years ago following a road traffic accident. A type and screen sample (ethylenediaminetetraacetic acid [EDTA] anticoagulant) is submitted to the blood bank. Blood group is reported as O positive and antibody screen is positive. Antibody identification is performed using the 11 cell panel shown above. Which antibody is present in the patient's sample?

1. Anti-C antibody
2. Anti-D antibody
3. Anti-E antibody
4. Anti-K antibody

C. Anti-E antibody is present in the given sample. Only 2 cells (3 and 6) show reaction; all other cells are negative. The pattern of reactivity matches with anti-E antibody. Answer A is incorrect because the negative reaction in cells 1, 2 and 11 helps to rule out anti-C antibody. Answer B is incorrect because anti-D antibody is ruled out as cells 1, 2, 4 and 11 did not show a reaction though D antigen is present. Answer D is incorrect because anti-K antibody is ruled out as cells 1 and 7 did not show a reaction though K antigen is present.

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Reference: Antibody identification & panel interpretation

A 60 year old man with a history of myelodysplastic syndrome presents with fatigue and pallor. He has received multiple transfusions in the past and has developed alloantibodies. His blood group is O positive. Antibody screening is done using a 3 cell panel that is positive (3+) in the first 2 cells. What is the best strategy to ensure that he receives compatible blood?

1. Perform antibody identification and administer antigen negative blood
2. Transfuse autologous blood
3. Transfuse O negative blood only
4. Transfuse O positive blood only

A. Perform antibody identification and administer antigen negative blood. Antibody identification should be done for this patient to identify the alloantibodies present. Once alloantibodies are identified, corresponding antigen negative units should be transfused into this patient. Answer B is incorrect because autologous blood cannot be transfused as the patient is suffering from myelodysplastic syndrome and requires frequent transfusions. Answers C and D are incorrect because transfusing O positive or O negative blood without performing antibody identification and antigen matching may result in acute or delayed hemolytic transfusion reaction.

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Reference: Antibody identification & panel interpretation