MLT GlobeBlood Banking: ABO system – page 4
116 Blood Banking MCQs on ABO system with answers and explanations.
An 85-year-old group O patient shows weak or no reactions with A1 and B cells in reverse typing. The best first step to resolve this is:
The elderly, newborns and people with low immunoglobulins may have weak ABO antibodies. Longer incubation at room temperature or 4 °C, with an autocontrol and O cells as controls, strengthens the reactions.
The H gene (FUT1) encodes an enzyme that adds which sugar to the precursor chain on red cells?
FUT1 fucosyltransferase adds L-fucose to the terminal galactose of type 2 precursor chains, making H antigen, the substrate for A and B transferases.
Expression of A, B and H substances in saliva and other secretions is controlled mainly by which gene?
The Se gene (FUT2) makes H on type 1 chains in secretory tissues. FUT1 controls H on red cells; without Se, no soluble ABH is secreted even if FUT1 is normal.
Saliva from a group A secretor is tested by hemagglutination inhibition. Which soluble substances will it contain?
A secretor of group A secretes A substance plus unconverted H substance. B substance is absent because the person lacks the B transferase.
Why is ABO hemolytic disease of the newborn seen mostly in babies of group O mothers?
Group O people have anti-A,B with a significant IgG component, which crosses the placenta. In group A and B mothers, anti-B or anti-A is mostly IgM and does not cross.
A patient with multiple myeloma has extra positive reactions with both A1 and B reagent cells. Cells look like stacks of coins under the microscope. The best way to resolve this is:
Raised globulins cause rouleaux, which mimics agglutination. Replacing plasma with saline disperses rouleaux while true agglutination remains. Enzyme treatment would increase, not remove, the false reactions.
A group A patient has a positive autocontrol at room temperature and agglutinates both A1 and B reagent cells weakly. Forward typing gives weak reactions with anti-B as well. The most likely cause is:
A strong cold autoagglutinin coats the patient's cells (causing false forward reactions) and reacts with all reagent cells. Washing cells in warm saline and prewarming the reverse type help resolve it.
A group A patient was given group O red cells in an emergency. Next day the red cells show a mixed-field reaction with anti-A. The most likely explanation is:
After transfusion of group O cells, a mixture of the patient's A cells and donor O cells gives mixed-field agglutination with anti-A. Weak subgroups can give mixed field, but the recent transfusion explains it here.
A cord blood sample gives weak nonspecific agglutination in all ABO forward-typing tubes. What is the most likely cause?
Wharton's jelly from the umbilical cord can cause nonspecific clumping of cord cells. Washing the cells several times in saline removes it.
A patient with acute myeloid leukemia was typed as group A last year. Today the cells react only weakly with anti-A, and the reverse typing is unchanged. The most likely explanation is:
Hematologic malignancies, especially leukemias, can reduce A or B antigen expression (a group II discrepancy). Antigen strength often returns with remission.
A group A patient needs fresh frozen plasma. Which plasma groups are compatible?
Plasma must not contain antibody against the recipient's antigens. Group A plasma (anti-B) and AB plasma (no antibody) are safe; group O plasma contains anti-A.
Anti-A1 is found more often in people of which phenotype?
Anti-A1 occurs in a small minority of A2 people but in a much larger proportion (about a quarter or more) of A2B people. A1 and A1B people do not make anti-A1.
Which statement best describes the difference between A1 and A2 red cells?
A1 cells carry many more A antigen sites, and the A1 transferase is more efficient. The differences are both quantitative and qualitative. A2 cells have more H, not less.
Parents with genotypes AO and BO have a child. Which child phenotypes are possible?
Each parent can pass A or O, and B or O. Combinations give AB, AO (A), BO (B) and OO (O), so all four phenotypes are possible.
A group O mother and a group AB father can have children of which ABO groups?
The mother gives O; the father gives A or B. Children are AO (group A) or BO (group B). Group O or AB children would not be expected.
During reverse typing, the supernatant in the B-cell tube is clear red and no cell button remains. How should this be interpreted?
ABO antibodies can activate complement and lyse reagent cells when serum is used. Hemolysis is a positive reaction and is recorded as such.
Why are A1 cells, not A2 cells, used as the routine A reagent cell for reverse typing?
A1 cells carry the most A antigen, so they reliably detect anti-A. A2 cells are used only when checking for anti-A1.
A group A patient with a bowel infection shows a new weak reaction with anti-B. Which finding supports acquired B rather than true group AB?
In acquired B, bacterial deacetylase makes A-antigen GalNAc look like galactose; the patient's own anti-B does not recognise it. Acidified anti-B stops reacting, and secretor saliva contains A, not B, substance.
Red cells show typical mixed-field agglutination with anti-A and anti-A,B, and the saliva of this secretor contains A substance. The most likely A subgroup is:
A3 is characterised by mixed-field agglutination with anti-A and anti-A,B, and secretors have A in saliva. Ax cells usually react better with anti-A,B than anti-A and are not typically mixed-field.
How does treatment of red cells with ficin affect their agglutination by anti-A and anti-B?
ABH antigens are carbohydrates and are not destroyed by proteases. Enzymes remove sialic acid and lower surface charge, so ABO reactions become stronger.