MLT GlobeBlood Banking: Rh system
79 Blood Banking MCQs on Rh system with answers and explanations.
The D antigen tested in routine blood typing belongs to which blood group system?
D is the most immunogenic Rh antigen and decides RhD-positive or -negative status. ABO antigens are A and B; Kell and Duffy are separate systems.
Antibodies to Rh antigens (e.g., anti-D) are characteristically:
Rh antibodies arise after transfusion or pregnancy, are IgG, react best at 37 °C and usually need the antiglobulin phase.
An RhD-positive patient needs red cells. Which donors are suitable?
The D-positive recipient has no reason to form anti-D, so D-negative cells are safe too; they are saved for D-negative patients.
Which ABO/RhD type is the classic universal recipient for red cells?
AB D-positive recipients have no anti-A, anti-B or reason to form anti-D, so can receive red cells of any ABO and RhD type.
Rh antigens are carried on which type of red cell membrane structure?
RhD and RhCE are nonglycosylated proteins that cross the membrane about 12 times. This is why Rh antigens are protein-based, unlike carbohydrate ABO and Lewis antigens.
The RHD and RHCE genes are located on which chromosome?
RHD and RHCE are closely linked on the short arm of chromosome 1. Chromosome 9 carries ABO; chromosome 4 carries MNS genes.
After A and B, which red cell antigen is the most immunogenic?
D is the most immunogenic non-ABO antigen; a large proportion of D-negative people exposed to D-positive red cells make anti-D. K is next most immunogenic.
In Wiener notation, the haplotype R1 corresponds to which Fisher-Race antigens?
R1 = DCe, R2 = DcE, R0 = Dce, and r' = dCe. Capital R shows D is present; the subscript or prime shows C/E antigens.
How does treatment of red cells with proteolytic enzymes such as papain affect Rh antigen reactions?
Enzymes remove sialic acid-rich glycoproteins, reduce surface charge and expose Rh antigens, so Rh antibody reactions are stronger.
Routine antenatal Rh immune globulin for a nonsensitized D-negative woman is usually given at about:
Antenatal RhIG is given at about 28 weeks, because most sensitizing fetal bleeds happen in the third trimester.
A 25-year-old D-negative woman needs emergency red cells before her type is fully confirmed. The best choice is:
Females of childbearing potential receive group O, D-negative red cells in emergencies to avoid anti-D and future HDFN.
A D-negative woman received antenatal RhIG at 28 weeks. She now delivers a D-positive baby. What is needed?
Antenatal RhIG does not replace the postpartum dose. After a D-positive birth she needs a fetomaternal hemorrhage screen and at least one dose.
Rh antigens are expressed on:
Rh proteins are erythroid-specific. This is why D-positive platelets cause sensitization only through contaminating red cells.
Compared with ABO antigens, Rh antigens on fetal and newborn red cells are:
Rh antigens are well expressed early in fetal life, which is why Rh antibodies can cause severe fetal disease. ABO antigens are weaker at birth.
Apart from anti-D, which Rh antibody most often causes severe hemolytic disease of the fetus and newborn?
Anti-c is the Rh antibody after anti-D most often linked to severe HDFN. Anti-C and anti-e usually cause mild disease.
A donor types D−, C−, c+, E−, e+. The genotype is:
No D, C or E is present, so both haplotypes must be dce. r′ would add C and r″ would add E.
In Wiener notation, the haplotype r′ corresponds to:
Lower-case r means D-negative; the prime (′) indicates C. So r′ is dCe, while r″ is dcE and ry is dCE.
Testing cell-free fetal DNA in maternal plasma for RHD is used mainly to:
Non-invasive fetal RHD genotyping avoids unnecessary RhIG when the fetus is D-negative and helps manage immunized women.
Rh immune globulin is prepared from:
RhIG is concentrated IgG anti-D fractionated from pooled plasma of immunized donors who have high-titer anti-D. D-positive donors cannot make anti-D.
The first D-positive baby of a previously unsensitized D-negative woman is usually not affected by anti-D HDFN because:
Most fetal bleeds large enough to immunize happen at delivery, and a primary response makes little IgG. Later D-positive pregnancies trigger a strong secondary IgG response.