CSMLS - Canadian Society for Medical Laboratory Science Transfusion Science: ABO Discrepancies Questions and Answers

Question 1

A patient's forward grouping shows agglutination with Anti-A and weak (1+) agglutination with Anti-B.
The reverse grouping shows agglutination with B cells only.
The patient's diagnosis is a severe gastrointestinal infection caused by a gram-negative bacteria.
What is the MOST likely cause of this ABO discrepancy?

Accepted Answer

Acquired B antigen

Answer

A subgroup with anti-B alloantibody

Answer

Recent transfusion of group B red cells

Answer

Cold autoantibody interference

Question 2

A technologist performs ABO grouping on a 92-year-old patient. The results are: Anti-A: 0, Anti-B: 4+, A1 Cells: 0, B Cells: 1+. Which of the following is the most appropriate first step to resolve this discrepancy?

Accepted Answer

Incubate the patient's plasma with reagent cells at room temperature or 4°C.

Answer

Perform an antibody screen to identify the unexpected antibody.

Answer

Use Dolichos biflorus lectin to test for A1 subgroup.

Answer

Wash the patient's red cells with warm saline and repeat the forward grouping.

Question 3

A patient's ABO typing results are as follows: Anti-A: 4+, Anti-B: 4+, A1 Cells: 2+, B Cells: 2+. All tubes, including the autocontrol, show agglutination at the immediate spin phase. Microscopic examination reveals rouleaux. What is the best technique to resolve this discrepancy?

Accepted Answer

Perform saline replacement on the reverse grouping tubes.

Answer

Perform a Direct Antiglobulin Test (DAT).

Answer

Adsorb the cold autoantibody from the plasma.

Answer

Test the patient's cells with anti-A1 lectin.

Question 4

A discrepancy is observed where the forward grouping suggests Group O (No agglutination with Anti-A or Anti-B), but the reverse grouping suggests Group A (agglutination with B cells only). The patient has a history of leukemia. What is the most likely cause of this discrepancy?

Accepted Answer

Weakened A antigen expression due to malignancy.

Answer

Presence of a potent cold autoantibody.

Answer

Transfusion of non-group specific plasma.

Answer

Chimerism from a recent stem cell transplant.

Question 5

Which of the following scenarios would most likely result in a mixed-field reaction in the forward ABO grouping?

Accepted Answer

A Group B patient recently transfused with Group O red blood cells.

Answer

A Group A patient with hypogammaglobulinemia.

Answer

A Group O patient with a strong cold autoantibody.

Answer

A Group AB patient with multiple myeloma.

Question 6

The forward type of a patient is Group A, but the reverse type shows an unexpected reaction with A1 cells, suggesting Group O. The patient is a healthy 25-year-old blood donor. What is the most probable cause for this discrepancy?

Accepted Answer

The patient is an A2 subgroup with anti-A1.

Answer

The patient has the Bombay phenotype (Oh).

Answer

The patient has an acquired B antigen.

Answer

There is rouleaux formation interfering with the test.