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

The 'Acquired B' phenomenon occurs in group A individuals, often with gastrointestinal diseases or gram-negative septicemia. Bacterial enzymes modify the A antigen (N-acetyl-D-galactosamine) to a structure that resembles the B antigen (D-galactose), causing a weak reaction with some anti-B reagents. [2, 6, 8] The patient's own anti-B does not react with this 'B-like' antigen, so the reverse group is consistent with a group A individual. [6, 8]

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

This is a Group 1 discrepancy, characterized by weak or missing antibodies in the reverse grouping. [4] This is common in elderly patients due to decreased antibody production. [4] To enhance the weak reaction, incubating the patient's plasma with the reagent A1 and B cells at lower temperatures (room temperature or 4°C) can help facilitate antibody binding and resolve the discrepancy. [2, 4]

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

This is a classic presentation of a Group 3 discrepancy caused by rouleaux formation, often due to abnormal plasma proteins (e.g., in multiple myeloma). Rouleaux causes non-specific aggregation of red cells. The saline replacement technique resolves this by dispersing the rouleaux; the technologist removes the patient's plasma and replaces it with saline. True agglutination will remain, while rouleaux will disperse. [2, 5, 9]

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

This is a Group 2 discrepancy, characterized by weak or missing antigens in the forward grouping. [4] Certain diseases, particularly hematologic malignancies like leukemia, can suppress the expression of ABO antigens on red blood cells, leading to weaker-than-expected or negative reactions in the forward type. [3, 4] The reverse grouping, which reflects the patient's true ABO antibodies, remains as expected for their actual blood group.

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 mixed-field reaction shows two distinct cell populations: one agglutinated and one unagglutinated. This is a hallmark of a recent transfusion with a different, compatible ABO group. A Group B patient receiving Group O red cells will have both their own B-antigen-positive cells (which will agglutinate with Anti-B) and the transfused O cells (which will not), creating a mixed-field appearance. [3, 4, 11]

CSMLS - Canadian Society for Medical Laboratory Science Practice Test

CSMLS - Canadian Society for Medical Laboratory Science Practice Test

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