MLT GlobeBlood Banking: Rh system – page 4
79 Blood Banking MCQs on Rh system with answers and explanations.
A European donor's red cells type D+, C+, E−, c+, e+. What is the most probable Rh genotype?
Presence of C and c means one C and one c haplotype; E absent. The commonest combination is R1 (DCe) with r (dce). R0r' gives the same phenotype but is much rarer.
A European donor's red cells type D+, C−, E−, c+, e+. What is the most probable genotype?
C and E are absent, so both haplotypes are ce. At least one carries D. Because r is very common in Europeans and R0 is rare, R0r is more probable than R0R0.
Red cells lacking all Rh antigens (Rhnull) typically show:
Rh proteins, with RHAG, maintain membrane integrity. Rhnull cells are stomatocytic and spherocytic with shortened survival, causing mild hemolytic anemia.
A pregnant woman types as serologic weak D. RHD genotyping shows weak D type 2. How should she be managed?
People with weak D types 1, 2 or 3 do not make alloanti-D, so they can be managed as D-positive. RHD genotyping avoids unnecessary RhIG and saves D-negative units.
Red cells type D-negative by direct agglutination and by the indirect antiglobulin test, but D is shown by adsorption–elution. This phenotype is:
Del cells carry so few D sites that only adsorption–elution detects them. Del is relatively common among D-negative East Asians.
With low-protein monoclonal anti-D, a separate negative control is required when the patient types as:
A negative anti-A or anti-B tube serves as a control for spontaneous agglutination. In group AB, D-positive samples every tube is positive, so a separate control is needed.
A plasma antibody reacts with D+C− cells and D−C+ cells, but not D−C− cells. Adsorption–elution studies show one antibody reacting with both. The specificity is:
G antigen is present on almost all cells carrying D or C. Anti-G mimics anti-D + anti-C; adsorption–elution separates them. The distinction matters because true anti-D shows RhIG failure.
An antibody reacts strongly with D-positive and weakly with D-negative adult cells. It does not react with DTT-treated cells but is not reduced by ficin. The most likely specificity is:
LW antigens are stronger on D-positive cells and are destroyed by DTT but resist enzymes. Rh antigens like D are not affected by DTT.
An R1R1 patient has anti-c. Which red cell units are most appropriate for transfusion?
R1R1 people lack c and E, and anti-E often accompanies anti-c or develops later. Giving R1R1 (c−E−) units prevents both. C-negative units would be c-positive.
A D-negative mother with anti-D delivers a baby whose cord cells type D-negative but have a strongly positive DAT with anti-IgG. The most likely explanation is:
Heavy coating with maternal IgG anti-D can block D sites so monoclonal anti-D cannot bind (blocked D). Gentle heat elution or RHD genotyping shows the true type.
A pregnant woman types weak D. RHD genotyping shows weak D type 1. How should she be managed?
People with weak D types 1, 2 or 3 do not make allo-anti-D, so they can receive D-positive blood and do not need RhIG. This is the AABB/CAP recommended approach.
The regulator type of Rhnull is caused by mutations in which gene?
RhAG is needed to carry Rh proteins to the membrane, so RHAG mutations give the regulator Rhnull type with normal RH genes. The amorph type is due to inactive RHCE with RHD deleted.
Monoclonal IgM anti-D reagents for patient typing are chosen so that they do NOT agglutinate partial DVI cells. Why?
DVI is the partial D most likely to make anti-D. Typing such patients as D-negative protects them; donor reagents, by contrast, should detect DVI.
Which of these Rh haplotypes is the rarest?
ry (dCE) is extremely rare in all populations. r′ and r″ are each about 1% in Europeans, and R0 is common in people of African descent.
Anti-f (anti-ce) reacts with red cells that carry:
f is a compound antigen made when c and e are in cis. R1R2 cells have c and e in trans and are f-negative.
A Kleihauer-Betke test gives an unexpectedly high fetal cell count, but flow cytometry with anti-D shows very few D-positive cells. Which maternal condition best explains this?
Maternal cells containing HbF resist acid elution and are counted as fetal cells. Anti-D flow cytometry counts only the D-positive fetal cells.
A rosette test on a D-negative mother's postpartum sample is falsely positive most often when:
Maternal weak D cells bind anti-D and form rosettes with indicator cells throughout the sample. A weak D baby tends to cause a false negative instead.
The E and e antigens differ by:
E/e is due to Pro226Ala in RhCE. C/c differ by several amino acids (mainly Ser103Pro) on the same RhCE protein.
An R2R2 patient has anti-e. About what proportion of donors of European descent are e-negative?
The e antigen is present in about 98% of Europeans, so only about 2% of donors are e-negative, making compatible units hard to find.