Special tests: column agglutination

5 ASCP MLS practice questions on Special tests: column agglutination, part of Blood Banking. The first 5 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

   Why does an anti-IgG gel card need no cell washing and no IgG-coated check cells?

   1. AGel tests detect only IgM antibodies
   2. BCheck cells are built into each well
   3. CFree IgG stays above the gel, away from the AHG
   4. DThe gel in these cards contains no anti-human globulin

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   Answer: C · Free IgG stays above the gel, away from the AHG

   In the gel test, cells and plasma are incubated above the gel, and centrifugation pulls only the red cells down into the gel containing anti-IgG. Unbound globulin in the plasma stays above the gel and cannot neutralize the reagent. This replaces the washing step of the tube test. Without washing there is also no risk of losing weakly bound antibody.

   • A: Gel AHG cards detect IgG antibodies.
   • B: No check cells are included; they are not needed because neutralization cannot occur.
   • D: The AHG card's gel does contain anti-IgG.

2. Question 2 · Medium

   A gel card well shows a band of red cells at the top and a button at the bottom. This is read as:

   1. AA 4+ reaction
   2. BMixed field
   3. CA negative reaction
   4. DHemolysis

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   Answer: B · Mixed field

   A top band with a separate button means some cells were agglutinated and others were not. This mixed-field pattern points to two red cell populations, for example after transfusion of a different group, after an ABO-mismatched transplant, or in an A3 subgroup. The history explains most cases. It must be recorded and investigated, not graded as a single result.

   • A: A 4+ reaction has all cells at the top and no button.
   • C: A negative reaction has all cells in the button.
   • D: Hemolysis shows as clear red fluid and loss of cells, not a band and a button.

3. Question 3 · Easy

   In the gel (column agglutination) test, the strongest (4+) reaction appears as:

   1. AA band of red cells at the top of the gel
   2. BA button of red cells at the bottom
   3. CNo red cells visible in the column
   4. DRed cells spread evenly through the gel

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   Answer: A · A band of red cells at the top of the gel

   During centrifugation, agglutinated cells are too large to pass through the gel particles. Large agglutinates stay at the top as a solid band, a 4+ reaction. Smaller agglutinates are caught lower down, giving weaker grades. Unagglutinated cells pass through and form a button at the bottom, a negative result.

   • B: A button at the bottom is a negative reaction.
   • C: The red cells are always visible somewhere in the column.
   • D: Cells spread through the gel show a weaker positive, not 4+.

4. Question 4 · Easy

   The anti-IgG gel card shows a patient's plasma tested with six panel cells. Which cell gives a 2+ reaction?

   

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   1. ACell 3
   2. BCell 5
   3. CCell 4
   4. DCell 1

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   Answer: C · Cell 4

   In column agglutination the grade depends on how far the agglutinates travel into the gel. A 4+ is a solid band on top (cell 5), and a 3+ stays mostly in the upper part (cell 1). A 2+ is spread through the length of the gel (cell 4), and a 1+ is small agglutinates in the lower half with some free cells at the bottom (cell 3); a negative is a button of cells at the bottom (cells 2 and 6).

   • A: Small agglutinates in the lower half with a button at the bottom are a 1+ reaction.
   • B: A solid band of cells on top of the gel is a 4+ reaction.
   • D: Agglutinates held in the upper part of the gel are a 3+ reaction.

5. Question 5 · Medium

   Before an emergency transfusion 2 days ago, a 30-year-old man typed group A, D-negative. Today's gel card is shown. Which red cells did he most likely receive?

   

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   1. AGroup A, D-negative
   2. BGroup A, D-positive
   3. CGroup O, D-negative
   4. DGroup O, D-positive

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   Answer: D · Group O, D-positive

   Mixed field, a band of agglutinated cells on top of the gel with a button of free cells at the bottom, means two red cell populations. In the anti-A well his own A cells agglutinate while the transfused cells stay free, so the donor cells lacked A (group O). In the anti-D well the transfused cells agglutinate while his own D-negative cells pass through, so the donor cells were D-positive. He should be followed for anti-D, and D-negative red cells used again once supply allows.

   • A: Group A, D-negative cells would give anti-A 4+ and anti-D 0, his original pattern.
   • B: Group A donor cells would agglutinate with anti-A, giving a full 4+ band, not mixed field.
   • C: D-negative donor cells would leave the anti-D well negative, as before transfusion.