A group A patient with chemotherapy-induced thrombocytopenia has had six group O apheresis platelet units this week. Today: anti-A 4+, anti-B 0; A1 cells 1+, A2 cells 1+, B cells 4+. The cells react with Dolichos lectin, the antibody screen is negative and the DAT is weakly positive. The most likely cause is:

Passive anti-A from the platelet plasma

Rouleaux from raised plasma proteins

Two months after a group A hematopoietic stem cell transplant, a group O recipient types: anti-A 1+ mixed field, anti-B 0; A1 cells 2+, B cells 4+. Which components suit this stage?

Group O red cells with group A or AB plasma

Group A red cells with group A plasma

Group A red cells with group O or AB plasma

Group O red cells with group O plasma

Which technical error can make the forward ABO grouping falsely negative?

A red cell suspension that is too heavy

Reagent contaminated with bacteria

Dirty glass tubes containing small particles

Centrifuging the tubes for too long

ABO system and grouping discrepancies

27 DOH Abu Dhabi (HAAD) lab licensing practice questions on ABO system and grouping discrepancies, part of Blood Banking. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Easy
The H antigen, on which the A and B transferases build, gets its specificity from which terminal sugar?
1. AN-acetylgalactosamine
2. BN-acetylglucosamine
3. CL-fucose
4. DD-galactose
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Answer: C · L-fucose
The H gene (FUT1) codes for a fucosyltransferase that adds L-fucose to the end galactose of the precursor chain, making H antigen. The A transferase then adds N-acetylgalactosamine, and the B transferase adds D-galactose, to the H antigen. Group O people have no active A or B transferase, so their cells keep the most H. Without fucose, as in the Bombay phenotype, A and B cannot be made even when the A or B gene is present.
- A: N-acetylgalactosamine is the sugar the A transferase adds to make A antigen.
- B: N-acetylglucosamine is part of the precursor chain, not the H-specific sugar.
- D: D-galactose is the sugar the B transferase adds to make B antigen.
Question 2 · Hard
A group A patient with chemotherapy-induced thrombocytopenia has had six group O apheresis platelet units this week. Today: anti-A 4+, anti-B 0; A1 cells 1+, A2 cells 1+, B cells 4+. The cells react with Dolichos lectin, the antibody screen is negative and the DAT is weakly positive. The most likely cause is:
1. ARouleaux from raised plasma proteins
2. BPassive anti-A from the platelet plasma
3. CA cold-reacting alloantibody
4. DAnti-A1 in an A2 patient
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Answer: B · Passive anti-A from the platelet plasma
Each apheresis platelet unit carries about 200-300 mL of donor plasma, and group O plasma contains anti-A and anti-B. Repeated group O platelets can give a group A patient enough passive anti-A to react weakly with A cells in the reverse grouping, and sometimes a positive DAT or hemolysis. The reaction with A2 cells and the A1 type of the patient's cells rule out anti-A1, and the negative screen makes another cold alloantibody unlikely. ABO-identical platelets, or units with low anti-A titers, reduce the problem.
- A: Rouleaux would not explain a weak reaction confined to the A cells.
- C: A negative antibody screen makes another cold alloantibody unlikely.
- D: The cells are A1 (Dolichos positive), and anti-A1 would not react with A2 cells.
Question 3 · Hard
An A2B patient has anti-A1 that reacts at 37 °C and in the antiglobulin phase. Red cells are needed. Which units are suitable?
1. AGroup B or group O red cells
2. BUnselected group AB red cells
3. CUnselected group A red cells
4. DGroup A1 or A1B red cells
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Answer: A · Group B or group O red cells
Anti-A1 is usually a weak cold IgM antibody of no clinical importance, but when it reacts at 37 °C it can shorten the survival of A1 cells. An A2B patient has no anti-B, so group B and group O red cells, which lack A1, are compatible; A2 or A2B units are also suitable when available. Most group A and AB units are A1 or A1B and would react. Plasma for this patient should still be group AB.
- B: Most group AB units are A1B and would be incompatible.
- C: About 80% of group A units are A1 and would be incompatible.
- D: A1 and A1B cells carry the A1 antigen that the antibody targets.
Question 4 · Hard
Two months after a group A hematopoietic stem cell transplant, a group O recipient types: anti-A 1+ mixed field, anti-B 0; A1 cells 2+, B cells 4+. Which components suit this stage?
1. AGroup A red cells with group A plasma
2. BGroup A red cells with group O or AB plasma
3. CGroup O red cells with group A or AB plasma
4. DGroup O red cells with group O plasma
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Answer: C · Group O red cells with group A or AB plasma
The mixed-field A reaction shows donor-derived A cells appearing, but the recipient still makes anti-A. Red cells must be compatible with that anti-A, so group O red cells are given. Plasma and platelets must not add anti-A against the engrafting A cells, so group A or AB plasma is used. Red cells change to group A only when anti-A is no longer detectable and the forward type shows the donor group.
- A: The recipient's remaining anti-A would destroy group A red cells.
- B: Group A red cells would meet the recipient's anti-A, and group O plasma adds more.
- D: Group O plasma carries anti-A against the engrafting A cells.
Question 5 · Medium
Which technical error can make the forward ABO grouping falsely negative?
1. AReagent contaminated with bacteria
2. BA red cell suspension that is too heavy
3. CDirty glass tubes containing small particles
4. DCentrifuging the tubes for too long
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Answer: B · A red cell suspension that is too heavy
With too many red cells, the reagent antibody is spread over too many antigen sites, so agglutination is weak or absent. Under-centrifuging, forgetting to add the reagent and shaking the cell button too hard also cause false negatives. Over-centrifuging, contaminated reagents and dirty tubes tend to cause false positives instead. Cell suspensions are therefore made to the strength the method specifies.
- A: Bacterial contamination can cause false-positive clumping.
- C: Particles in dirty tubes can be mistaken for agglutination.
- D: Over-centrifuging packs the cells so tightly that they may look agglutinated.
Question 6 · Hard
A patient's red cells react only very weakly with anti-A and anti-A,B. Saliva studies: saliva plus anti-A, then A1 cells, no agglutination; saliva plus anti-B, then B cells, 4+; saliva plus anti-H lectin, then O cells, no agglutination. The saliva contains:
1. AB and H substances
2. BA and H substances
3. CH substance only
4. DNo ABH substances
Answer and explanation in LearnFree account
Question 7 · Hard
A healthy donor types: anti-A 1+, anti-B 4+; A1 cells 4+, A2 cells 3+, B cells 0; autocontrol 0. Anti-A from a different monoclonal clone gives no reaction with the cells. The most likely explanation is:
1. AThe B(A) phenotype
2. BA cis-AB allele
3. CAcquired B antigen
4. DA weak A subgroup in an AB person
Answer and explanation in LearnFree account
Question 8 · Medium
Weak or missing reactions in the reverse grouping are most expected in which patients?
1. APatients with colon cancer or gut infections
2. BNewborns, the elderly and those with hypogammaglobulinemia
3. CPatients with marked rouleaux formation
4. DPatients with cold agglutinin disease
Answer and explanation in LearnFree account
Question 9 · Hard
A patient with advanced pancreatic carcinoma has red cells tested while suspended in her own plasma: anti-A 1+, anti-B 0; A1 cells 0, B cells 4+. After the cells are washed three times in saline, anti-A gives 4+. The weak first reaction was most likely due to:
1. ASoluble A substance neutralizing the reagent
2. BCold autoantibody coating the cells
3. CRouleaux caused by the tumor proteins
4. DA weak A subgroup such as A3
Answer and explanation in LearnFree account
Question 10 · Medium
A correctly labeled routine sample gives forward and reverse ABO groupings that do not agree. What is the first step?
1. ASend the sample away for ABO genotyping
2. BTest the plasma against a full antibody panel
3. CCheck the records and repeat the tests on the same sample
4. DReport the forward grouping with a comment
Answer and explanation in LearnFree account
Question 11 · Easy
Among group A people of European ancestry, about what share belong to the A2 subgroup?
1. AAbout 1%
2. BAbout 80%
3. CAbout 50%
4. DAbout 20%
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Question 12 · Hard
Results: anti-A w+, anti-A,B 2+, anti-B 0; A1 cells 2+, A2 cells 0, B cells 4+; O cells and autocontrol 0. The most likely interpretation is:
1. AGroup O with a cold alloantibody
2. BA2 with anti-A1
3. CAx with anti-A1
4. DA3 with mixed-field reactions
Answer and explanation in LearnFree account
Question 13 · Medium
Why does a newborn's forward ABO grouping often give weaker reactions than an adult's?
1. AWharton's jelly coats the infant's red cells
2. BA and B antigens are not yet fully developed
3. CFetal hemoglobin weakens the agglutination
4. DMaternal anti-A and anti-B block the sites
Answer and explanation in LearnFree account
Question 14 · Medium
In a tube test, mixed-field agglutination looks like:
1. ASmall agglutinates among many free red cells
2. BUniform fine clumping of all the red cells
3. CStacks of red cells like piles of coins
4. DHemolysis with no visible agglutinates
Answer and explanation in LearnFree account
Question 15 · Medium
A discrepancy between the forward and reverse grouping cannot be resolved today. How should the ABO group be recorded?
1. AAs undetermined until it is resolved
2. BAs the reverse grouping result
3. CAs group O until the discrepancy is resolved
4. DAs the forward grouping result
Answer and explanation in LearnFree account
Question 16 · Hard
Today's pretransfusion sample types group A, D-positive. The laboratory record shows group O, D-positive 2 years ago, and there has been no transplant. What should be done?
1. ACollect a new sample and investigate a wrong-blood-in-tube error
2. BIssue group A red cells and retest the sample later
3. CReport group A and correct the historical record
4. DReport group O, because the earlier record takes priority
Answer and explanation in LearnFree account
Question 17 · Medium
Which ABO group has the least unconverted H antigen on its red cells?
1. AA2
2. BO
3. CA1B
4. DA2B
Answer and explanation in LearnFree account
Question 18 · Easy
Which plant lectin is used to tell A1 red cells from A2 red cells?
1. ABandeiraea simplicifolia
2. BArachis hypogaea
3. CDolichos biflorus
4. DUlex europaeus
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Question 19 · Hard
A never-transfused adult types: anti-A 0, anti-B 0, anti-A,B 0; A1 cells 0, B cells 4+; screen and autocontrol 0. The A1 tubes stay negative after 30 minutes at room temperature. What is the best next step?
1. ARepeat the reverse grouping using A2 cells
2. BTest the red cells with Dolichos biflorus lectin
3. CAdsorb and elute anti-A from the red cells
4. DReport the group as O with a comment
Answer and explanation in LearnFree account
Question 20 · Medium
A patient of South Asian origin in an Abu Dhabi hospital is confirmed to have the Bombay (Oh) phenotype. Which red cells are compatible?
1. AOh red cells from Bombay donors
2. BGroup A2 red cells
3. CGroup O red cells
4. DWashed group O red cells
Answer and explanation in LearnFree account
Question 21 · Hard
A 28-year-old woman of Korean ancestry, never transfused, books at an Abu Dhabi antenatal clinic in her second pregnancy. She is well, with no infection. ABO results: anti-A 3+, anti-B 1+, anti-A,B 3+; A1 cells 0, B cells 1+. Group O screening cells and the autocontrol are negative at all phases, and the DAT is negative. A second sample collected the next day gives the same results. Her husband types group O, and their 4-year-old son types group O, with 4+ anti-A and 4+ anti-B in his reverse grouping and normal H on his cells. The most likely explanation is:
1. AA B(A) phenotype from a strong B enzyme
2. BA cis-AB allele paired with an O allele
3. CA weak B subgroup paired with an A allele
4. DAcquired B antigen from bacterial enzymes
Answer and explanation in LearnFree account
Question 22 · Hard
A 34-year-old woman has donated blood at an Abu Dhabi blood bank twice a year for 6 years. She has never been transfused, pregnant or given a transplant, and she is well. Every donation has given the same ABO results: anti-A mixed field (about 30% of cells agglutinated), anti-B 0, anti-A,B mixed field; A1 cells 0, B cells 4+. Saliva inhibition studies show H substance but no A substance. When the agglutinated cells are separated from the free cells, the agglutinated cells type Jk(a+b-) and the free cells type Jk(a-b+). She mentions that she has a twin brother. What is the most likely explanation?
1. ABlood group chimerism from her twin
2. BAn Ax subgroup with weak A antigen
3. CAn A3 subgroup with mixed-field A
4. DLoss of A antigen from a marrow disorder
Answer and explanation in LearnFree account
Question 23 · Hard
On a manual tube bench, a trainee refills the dropper bottles of A1 and B reagent red cells from new lots at 10:00; reagent QC was done at 08:00. Four patients with historical groups are then tested. Patient 1 (group A on record): anti-A 4+, anti-B 0; A1 cells 4+, B cells 0. Patient 2 (group B on record): anti-A 0, anti-B 4+; A1 cells 0, B cells 4+. Patient 3 (group O on record): anti-A 0, anti-B 0; A1 cells 4+, B cells 4+. Patient 4 (group AB on record): anti-A 4+, anti-B 4+; A1 cells 0, B cells 0. No sample is hemolyzed, and all four antibody screens, including an immediate-spin reading, are negative. The most likely cause is:
1. ACold alloantibodies in patients 1 and 2
2. BA1 and B cells placed in each other's bottles
3. CDeteriorated reagent cells from the new lots
4. DWrong-blood-in-tube errors in patients 1 and 2
Answer and explanation in LearnFree account
Question 24 · Easy
How should the forward and reverse grouping on the gel card shown be interpreted?
Figure: MedExams
1. AGroup AB, D-negative
2. BGroup A, D-negative
3. CGroup B, D-negative
4. DGroup B, D-positive
Answer and explanation in LearnFree account
Question 25 · Medium
A 52-year-old man, group A D-positive on record, received 4 units of red cells at another hospital 5 days ago. His new sample gives the gel card shown. Which units did he most likely receive?
Figure: MedExams
1. AGroup O, D-negative
2. BGroup O, D-positive
3. CGroup A, D-negative
4. DGroup AB, D-positive
Answer and explanation in LearnFree account

2 more ABO system and grouping discrepancies questions

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ABO system and grouping discrepancies

The H antigen, on which the A and B transferases build, gets its specificity from which terminal sugar?

An A2B patient has anti-A1 that reacts at 37 °C and in the antiglobulin phase. Red cells are needed. Which units are suitable?

Two months after a group A hematopoietic stem cell transplant, a group O recipient types: anti-A 1+ mixed field, anti-B 0; A1 cells 2+, B cells 4+. Which components suit this stage?

Which technical error can make the forward ABO grouping falsely negative?

A patient's red cells react only very weakly with anti-A and anti-A,B. Saliva studies: saliva plus anti-A, then A1 cells, no agglutination; saliva plus anti-B, then B cells, 4+; saliva plus anti-H lectin, then O cells, no agglutination. The saliva contains:

A healthy donor types: anti-A 1+, anti-B 4+; A1 cells 4+, A2 cells 3+, B cells 0; autocontrol 0. Anti-A from a different monoclonal clone gives no reaction with the cells. The most likely explanation is:

Weak or missing reactions in the reverse grouping are most expected in which patients?

A patient with advanced pancreatic carcinoma has red cells tested while suspended in her own plasma: anti-A 1+, anti-B 0; A1 cells 0, B cells 4+. After the cells are washed three times in saline, anti-A gives 4+. The weak first reaction was most likely due to:

A correctly labeled routine sample gives forward and reverse ABO groupings that do not agree. What is the first step?

Among group A people of European ancestry, about what share belong to the A2 subgroup?

Results: anti-A w+, anti-A,B 2+, anti-B 0; A1 cells 2+, A2 cells 0, B cells 4+; O cells and autocontrol 0. The most likely interpretation is:

Why does a newborn's forward ABO grouping often give weaker reactions than an adult's?

In a tube test, mixed-field agglutination looks like:

A discrepancy between the forward and reverse grouping cannot be resolved today. How should the ABO group be recorded?

Today's pretransfusion sample types group A, D-positive. The laboratory record shows group O, D-positive 2 years ago, and there has been no transplant. What should be done?

Which ABO group has the least unconverted H antigen on its red cells?

Which plant lectin is used to tell A1 red cells from A2 red cells?

A never-transfused adult types: anti-A 0, anti-B 0, anti-A,B 0; A1 cells 0, B cells 4+; screen and autocontrol 0. The A1 tubes stay negative after 30 minutes at room temperature. What is the best next step?

A patient of South Asian origin in an Abu Dhabi hospital is confirmed to have the Bombay (Oh) phenotype. Which red cells are compatible?

How should the forward and reverse grouping on the gel card shown be interpreted?

A 52-year-old man, group A D-positive on record, received 4 units of red cells at another hospital 5 days ago. His new sample gives the gel card shown. Which units did he most likely receive?