MLT GlobeBlood Banking: Antibody screen & identification – page 2
90 Blood Banking MCQs on Antibody screen & identification with answers and explanations.
Many laboratories omit the immediate-spin and room-temperature phases in the antibody screen mainly because:
Cold-reactive IgM antibodies such as anti-M, anti-P1 and anti-Lea are found in these phases and are rarely significant.
A healthy man who was never transfused has an antibody reacting at room temperature. The most likely specificity is:
Anti-M often occurs without red cell exposure and reacts in the cold. Anti-K, anti-Fya and anti-c are usually immune antibodies.
The chart listing which antigens are present on each reagent panel cell is called the:
The antigram (antigen profile sheet) lists the antigens on each panel cell. Reactions are compared with it to rule antibodies in or out.
Polyspecific antihuman globulin (AHG) reagent contains antibodies to:
Polyspecific AHG contains anti-IgG and anti-C3d, so it detects red cells coated with IgG, complement or both.
An antibody made against a red cell antigen that the person lacks, after transfusion or pregnancy, is called:
Alloantibodies react with foreign antigens the person lacks. Autoantibodies react with the person's own red cells.
When the antibody screen is positive, the next step is usually to:
A positive screen shows an unexpected antibody. Its specificity is found by testing the plasma against a panel of typed red cells.
The first stage of hemagglutination, in which antibody binds to red cell antigen, is called:
Agglutination has two stages: sensitization (antibody attaches to antigen) and lattice formation (antibody bridges cells to form visible clumps).
Red cell antibodies other than the expected anti-A and anti-B are called:
Antibody screening looks for unexpected antibodies, such as anti-D or anti-K, which are not normally present.
In a column (gel) agglutination test, a negative reaction appears as:
Unagglutinated cells pass through the gel during centrifugation and form a button at the bottom. Agglutinates are trapped at the top or within the gel.
A positive direct antiglobulin test indicates what?
The DAT detects in vivo sensitization of red cells, as in hemolytic disease of the newborn or autoimmune hemolysis. The indirect test detects serum antibodies binding in vitro.
A jaundiced newborn of a group O, RhD-negative mother is suspected of haemolytic disease. Which test on cord blood shows maternal antibody on the baby's cells?
A positive DAT confirms in-vivo coating of fetal cells by maternal IgG. The Kleihauer test quantifies fetomaternal haemorrhage in the mother.
Which antibody is notorious for showing dosage, fading in storage and causing delayed hemolytic transfusion reactions?
Kidd antibodies often drop to undetectable levels and then rise quickly after re-exposure, causing delayed hemolysis. They bind complement and react more strongly with homozygous cells.
Screening cells are chosen so that some are homozygous for antigens such as Jka, Fya and c. The main reason is to:
Weak antibodies with dosage (e.g. Kidd, Duffy, Rh) may react only with double-dose cells. Homozygous expression improves detection of these clinically significant antibodies.
Which antigen is NOT required on the set of reagent red cells used for antibody screening?
Screening cells must carry D, C, E, c, e, M, N, S, s, P1, Lea, Leb, K, k, Fya, Fyb, Jka and Jkb. Kpa is a low-prevalence antigen and is not required.
To confirm an antibody identification at p ≤ 0.05 by the classic 'rule of three', you need:
Three antigen-positive reactive cells and three antigen-negative nonreactive cells give a probability of about 1 in 20 that the pattern is due to chance. Reactive cells alone do not exclude random reactions.
A plasma antibody reacts at immediate spin and room temperature with panel cells 2, 5 and 8 but not at AHG. These three cells are the only M+N− cells. The most likely antibody is:
Cold reactivity that follows M antigen and is strongest with homozygous M+N− cells fits anti-M, which shows dosage. Anti-S and anti-Jka usually react at the AHG phase.
A never-transfused patient with warm autoimmune hemolytic anemia has pan-reactive plasma. Which method best detects underlying alloantibodies?
The patient's own cells, after removing bound autoantibody, adsorb only autoantibody and leave alloantibodies in the plasma. This is safe only when the patient has not been transfused recently.
A patient transfused 2 weeks ago has a warm autoantibody. Why should autologous adsorption NOT be used?
Donor cells still circulating in the sample may carry antigens that remove the patient's alloantibodies. Allogeneic (differential) adsorption with phenotyped cells is used instead, usually if transfusion was within about 3 months.
Ten days after transfusion, a patient's hemoglobin falls, and the DAT is positive with anti-IgG. The eluate reacts only with Jk(a+) cells. This indicates:
An alloantibody bound to transfused antigen-positive cells after a secondary (anamnestic) response is typical of a delayed hemolytic reaction. Autoantibody eluates usually react with all cells.
When preparing an eluate, the last wash of the cells is also tested. Its purpose is to show that:
If the last wash reacts, free plasma antibody remains and may give false eluate reactivity. A nonreactive last wash shows that the eluate contains only antibody removed from the cells.