Special techniques: enzymes, adsorption and elution

10 DOH Abu Dhabi (HAAD) lab licensing practice questions on Special techniques: enzymes, adsorption and elution, part of Blood Banking. The first 10 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   A patient with warm autoimmune hemolytic anemia was transfused 3 weeks ago. The plasma reacts with every panel cell and with the autocontrol. Which method is best for detecting alloantibodies hidden by the autoantibody?

   1. AAdsorption with phenotyped allogeneic red cells
   2. BAutoadsorption with the patient's ZZAP-treated cells
   3. CElution of the patient's own red cells
   4. DA repeat panel with ficin-treated cells

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   Answer: A · Adsorption with phenotyped allogeneic red cells

   After a recent transfusion the patient's circulation still holds donor red cells, and these could adsorb an alloantibody along with the autoantibody, so autoadsorption is avoided within about 3 months of transfusion. Allogeneic adsorption uses group O cells of known phenotype, often ZZAP- or enzyme-treated, to remove the autoantibody. An alloantibody stays in the plasma when the adsorbing cells lack its antigen, so the cells are chosen (or several are used) to cover the common clinically significant specificities. The adsorbed plasma is then tested against a panel.

   • B: Transfused donor cells in the sample could remove alloantibodies too.
   • C: An eluate shows what coats the cells, usually the autoantibody, not alloantibodies left in the plasma.
   • D: Ficin strengthens most warm autoantibodies, so the panel would still react with every cell.

2. Question 2 · Medium

   A laboratory proposes to screen patients' plasma with ficin-treated reagent cells only, to strengthen weak reactions. Which antibodies would this practice miss?

   1. AAnti-Fya and anti-M
   2. BAnti-K and anti-Kpa
   3. CAnti-Jka and anti-Jkb
   4. DAnti-c and anti-E

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   Answer: A · Anti-Fya and anti-M

   Ficin and papain cleave the membrane glycoproteins that carry the Duffy (Fya, Fyb) and MN antigens, so antibodies to them stop reacting with treated cells; S and s are weakened to a variable degree. Rh and Kidd reactions become stronger, and Kell antigens are not affected by these enzymes. Enzyme-treated cells are therefore used alongside untreated cells, never in place of them. Enzyme methods also pick up more cold and warm autoantibodies of little clinical importance.

   • B: Kell antigens resist ficin and papain, so anti-K and anti-Kpa are still detected.
   • C: Kidd antibodies react more strongly with enzyme-treated cells.
   • D: Rh antibodies such as anti-c and anti-E react more strongly with enzyme-treated cells.

3. Question 3 · Hard

   A plasma shows two antibody patterns. Pattern 1 reacts at the antiglobulin phase and becomes stronger with ficin-treated cells. Pattern 2 reacts at immediate spin and room temperature only, and disappears with ficin-treated cells. Which pair of antibodies fits best?

   1. AAnti-Fyb and anti-N
   2. BAnti-Jka and anti-M
   3. CAnti-Fya and anti-Lea
   4. DAnti-K and anti-P1

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   Answer: B · Anti-Jka and anti-M

   Kidd antibodies react at the antiglobulin phase and are enhanced by ficin, which fits pattern 1. Anti-M is usually a cold-reacting antibody, and the M antigen is destroyed by ficin, which fits pattern 2. Duffy antibodies would disappear with ficin, Lewis and P1 antibodies would get stronger, and Kell reactions would not change. Comparing untreated and enzyme-treated panels in this way is a simple tool for separating a mixture of antibodies.

   • A: Anti-N fits pattern 2, but anti-Fyb would disappear with ficin rather than get stronger.
   • C: Anti-Fya is destroyed by ficin, and anti-Lea is enhanced by it, so neither pattern fits.
   • D: Kell reactions are unchanged by ficin, and anti-P1 is enhanced rather than lost.

4. Question 4 · Hard

   Plasma with a warm autoantibody is split into three aliquots, each adsorbed with a different group O cell: cell 1 is Jk(a+b-), cell 2 is Jk(a-b+), cell 3 is Jk(a+b+). Only the aliquot adsorbed with cell 2 still reacts, and only with Jk(a+) panel cells. What is the best interpretation?

   1. AAlloanti-Jka is present with the autoantibody
   2. BAlloanti-Jkb is present with the autoantibody
   3. CThe adsorption with cell 2 was incomplete
   4. DThe autoantibody has anti-Jkb specificity

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   Answer: A · Alloanti-Jka is present with the autoantibody

   Each adsorbing cell removes the autoantibody, plus any alloantibody to antigens it carries. Cells 1 and 3 are Jk(a+), so they also remove anti-Jka, while cell 2 is Jk(a-) and leaves anti-Jka behind. The cell 2 aliquot reacting only with Jk(a+) cells therefore shows an alloanti-Jka under the autoantibody. Jk(a-) red cells should be selected, and adsorbing cells of different phenotypes are chosen so that each common alloantibody survives in at least one aliquot.

   • B: Cell 2 is Jk(b+), so it would have removed any anti-Jkb.
   • C: Leftover autoantibody would react with all panel cells, not only Jk(a+) ones.
   • D: Reactions only with Jk(a+) cells do not fit anti-Jkb, and the autoantibody has been removed.

5. Question 5 · Medium

   A patient's DAT is positive with anti-C3d and negative with anti-IgG. An acid eluate from these cells is most likely to show:

   1. ANo reactivity, since no IgG is on the cells
   2. BReactivity with A1 cells but not B cells
   3. CReactivity with I-positive cells only
   4. DReactivity with every panel cell

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   Answer: A · No reactivity, since no IgG is on the cells

   Elution recovers antibody that is still bound to the cells, which in practice means IgG. When the DAT shows complement only, as in cold agglutinin disease, the IgM that fixed the complement has already come off the cells at body temperature and during warm washing, leaving C3d behind. An eluate from such cells is therefore usually nonreactive and adds little. The workup focuses instead on the plasma, for example the thermal range and titer of a cold agglutinin.

   • B: Anti-A in an eluate would come with IgG on the cells, as in ABO hemolytic disease.
   • C: Cold IgM anti-I comes off the cells during warm washing, so it is not recovered in the eluate.
   • D: A panreactive eluate points to an IgG warm autoantibody, which would make the anti-IgG DAT positive.

6. Question 6 · Hard

   A group A patient received two group O apheresis platelet units. The next day the DAT is positive with anti-IgG, and an eluate is nonreactive with all group O panel cells. What is the best next step?

   1. AReport the eluate as negative and close the case
   2. BAdsorb the patient's plasma with allogeneic cells
   3. CTest the eluate with A1 and B reagent cells
   4. DRepeat the eluate test with ficin-treated panel cells

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7. Question 7 · Easy

   A laboratory needs to recover anti-A that is coating a patient's red cells so that it can be identified. Which procedure does this?

   1. AHeat elution at 56 °C
   2. BSaline replacement of the plasma
   3. CFicin treatment of the red cells
   4. DDTT treatment of the plasma

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8. Question 8 · Medium

   A patient who has not been transfused for years has a DAT positive with anti-IgG. The eluate reacts with every panel cell, while the plasma antibody screen is negative. What is the best interpretation?

   1. APassive antibody from a recent plasma infusion
   2. BAlloantibody to a high-prevalence antigen
   3. CAntibody carried over from incomplete washing
   4. DWarm autoantibody, with all of it bound to the cells

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9. Question 9 · Medium

   A patient who has never been transfused has a strong cold autoanti-I that may hide an alloantibody. Which conditions are used for a cold autoadsorption?

   1. AGroup O cord red cells at 37 °C
   2. BGroup O cord red cells at 4 °C
   3. CThe patient's own red cells at 37 °C
   4. DThe patient's own red cells at 4 °C

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10. Question 10 · Hard

    A 27-year-old D-negative (rr) woman is 26 weeks into her second pregnancy. Her first baby was D-positive, and she has never received Rh immune globulin. Her plasma reacts at the antiglobulin phase with R1R1 cells 3+, R2R2 cells 2+, r'r cells 2+ and rr cells 0. Further tests: plasma adsorbed with r'r cells is nonreactive with R2R2 cells; an eluate from those r'r cells reacts 2+ with R2R2 cells; plasma adsorbed with R2R2 cells still reacts 1+ with r'r cells. Which antibodies are present, and what does this mean for Rh immune globulin (RhIG) prophylaxis?

    1. AAnti-G only; she still needs RhIG
    2. BAnti-C and anti-G; she still needs RhIG
    3. CAnti-D and anti-C; RhIG is of no benefit
    4. DAnti-D and anti-G; RhIG is of no benefit

    Answer and explanation in LearnFree account