MLT GlobeBlood Banking: ABO system – page 2
116 Blood Banking MCQs on ABO system with answers and explanations.
Which sugar, when added to H substance, gives the A antigen its specificity?
The A transferase adds N-acetyl-D-galactosamine to the H antigen. D-galactose is the immunodominant sugar of the B antigen.
The B gene product is a transferase that adds which sugar to the H antigen?
The B galactosyltransferase attaches D-galactose to the H structure. N-acetyl-D-galactosamine is added by the A transferase, not the B transferase.
Naturally occurring anti-A and anti-B in a group A or group B adult are mainly of which class, and react best at what temperature?
ABO antibodies in group A and B people are mostly IgM, agglutinating saline-suspended cells at room temperature or colder, although they can also react and activate complement at 37 °C.
A trauma patient's ABO discrepancy cannot be resolved and he needs red cells immediately. Which red cells should be issued?
Until the discrepancy is resolved, group O red cells are given because they lack A and B antigens. Group AB red cells would be incompatible with anti-A or anti-B in the plasma.
A group B patient needs red cells, but no group B units are available. Which ABO group of red cells is the best alternative?
A group B patient has anti-A, so red cells must lack A antigen. Group O red cells lack both A and B and are compatible.
ABO antigens are important in solid organ transplantation mainly because they are:
ABH are histo-blood group antigens found on endothelium and many epithelial cells. ABO-incompatible grafts risk hyperacute rejection from recipient anti-A or anti-B.
Compared with adult red cells, ABO antigens on newborn red cells are:
A and B antigens are present at birth but weaker, as fewer branched chains are formed. Adult strength develops over the first few years of life.
Which genotypes are possible for a person who types as group A?
The A allele is dominant over O, so group A may be AA or AO. Routine serology cannot tell them apart; molecular testing or family studies are needed.
Most routine anti-A and anti-B typing reagents used today are:
Current ABO reagents are mostly mouse monoclonal IgM antibodies, which are standardized and strong. Human polyclonal sera were used in the past; lectins serve special purposes.
In tube ABO typing, a mixed-field reaction looks like:
Mixed field shows agglutinates alongside a large population of unagglutinated cells, indicating two cell populations. Coin-like stacking is rouleaux.
For routine tube ABO forward typing, red cells are usually tested as a suspension of what concentration and read after:
Standard tube ABO typing uses a 2–5% saline cell suspension, centrifuged immediately and read for agglutination. ABO IgM antibodies do not need incubation or AHG.
In people of European descent, about what proportion of group A individuals belong to subgroup A1?
Roughly 80% of group A people are A1 and about 20% are A2. A2 is the second most common subgroup, not the majority.
Which ABO group is the least common in nearly all populations?
Group AB needs both an A and a B allele, so it is the least frequent group worldwide. Group B is less common than A in Europeans but is still more common than AB.
Forward typing shows group O, but reverse typing gives no reaction with A1 or B cells. The patient has X-linked agammaglobulinemia. What causes the discrepancy?
Hypogammaglobulinemia gives weak or missing reverse reactions (a group I discrepancy). Rouleaux would cause extra positive reactions, not missing ones.
Many transfusion services require ABO typing on two separately collected samples before issuing non-group-O red cells. The main purpose is to:
A second independent sample shows whether the first tube was drawn from the wrong patient. It does not improve detection of weak subgroups.
In tube testing, a reaction with many small agglutinates and a turbid reddish background is graded as:
A 1+ reaction shows many small agglutinates in a turbid background. A 4+ reaction is one solid clump with a clear background.
On average, people of group O have lower plasma levels of:
VWF carries ABH antigens, and group O VWF is cleared faster, so levels are about 25% lower. This must be considered when interpreting VWF results.
A group B mother has a group AB child. Which alleged father can be excluded?
The child's A allele must come from the father. A group O man carries only O alleles, so he is excluded.
By convention, reagent anti-A and anti-B are coloured:
Anti-A contains a blue dye and anti-B a yellow dye, which helps prevent reagent mix-ups.
Daily quality control of anti-A and anti-B typing reagents is done by testing them with:
Each reagent must give the expected positive and negative results with known antigen-positive and antigen-negative cells. O cells alone show no positive reaction.