MLT GlobeBlood Banking: HDFN – page 2
56 Blood Banking MCQs on HDFN with answers and explanations.
In many laboratories, a maternal anti-D titer in which range is considered 'critical', prompting fetal monitoring for anemia?
A titer of 16 or 32 (set by each laboratory) is usually taken as critical. Below this, severe HDFN is unlikely and titers are simply repeated during pregnancy.
Which non-invasive test is now preferred to detect moderate to severe fetal anemia in an alloimmunized pregnancy?
An anemic fetus has lower blood viscosity and higher cardiac output, so MCA peak velocity rises. This Doppler test has largely replaced amniocentesis.
In the older Liley method, spectrophotometric analysis of amniotic fluid at 450 nm (ΔOD450) estimates:
Bilirubin absorbs at 450 nm, so the deviation at this wavelength reflects the degree of fetal hemolysis. Results are plotted by gestational age in zones.
A D-negative woman has anti-D. Which test on maternal plasma can determine whether the fetus is D-positive without invasive sampling?
Fetal DNA circulates in maternal plasma and can be tested for the RHD gene. If the fetus is D-negative, the pregnancy is not at risk from anti-D.
Which set of requirements fits red cells prepared for intrauterine transfusion in anti-D HDFN?
The cells must lack the antigen of the maternal antibody, be irradiated to prevent TA-GVHD, and be crossmatched with maternal plasma. They are also fresh, CMV-risk-reduced, HbS-negative and highly concentrated.
Cord red cells show agglutination in all tubes, including the control. The sample was taken by squeezing the cord. What is the likely cause and remedy?
Wharton's jelly from the cord can make cells stick together and give false agglutination. Washing the cells several times with saline removes it.
A D-negative mother received RhIG at 28 weeks. Her D-positive newborn has a weakly positive DAT and no anemia or jaundice. The best explanation is:
Some RhIG crosses the placenta and can weakly coat fetal D-positive cells. This rarely causes hemolysis; the mother is still eligible for postpartum RhIG.
Reconstituted whole blood for exchange transfusion in HDFN is usually prepared from group O red cells suspended in plasma of group:
Group AB plasma has no anti-A or anti-B, so it cannot harm the infant's cells whatever the infant's ABO group. Group O red cells are compatible with maternal anti-A and anti-B.
Why is hyperbilirubinemia rarely a problem for the fetus before birth in HDFN?
Unconjugated bilirubin passes to the mother and is cleared by her liver. After birth, the immature newborn liver cannot conjugate enough, so bilirubin rises quickly.
After anti-D, which Rh antibody most often causes severe HDFN?
Anti-c can cause severe HDFN requiring intrauterine or exchange transfusion. Anti-C, anti-e and anti-Cw usually cause mild disease.
Maternal IgG reaches the fetus by active transport across the placenta through which receptor?
FcRn on syncytiotrophoblast transports IgG, increasing sharply in the second and third trimesters. The polymeric Ig receptor carries IgA across mucosa, not placenta.
Blood is needed for exchange transfusion of a newborn with anti-D HDFN. Which sample is preferred for antibody screening and crossmatch?
Maternal plasma has a higher antibody concentration and a larger volume, so incompatibility is easier to detect. Cord plasma can be used if a maternal sample is unavailable.
A D-negative woman received antenatal RhIG at 28 weeks. At delivery, her antibody screen shows anti-D with a titer of 2. The baby is D-positive. What should be done?
A low anti-D titer after antenatal RhIG is usually passive. Unless active immunization is documented, postpartum RhIG should still be given.
A group O, D-negative woman carries a group A, D-positive fetus. Why is her risk of forming anti-D reduced?
ABO-incompatible fetal cells entering the maternal circulation are quickly destroyed by maternal anti-A or anti-B, so there is less chance of immunization to D.
What is the role of the rosette test after delivery?
The rosette test screens for a fetomaternal hemorrhage of about 10 mL or more of fetal blood. If positive, the bleed is quantified by Kleihauer-Betke or flow cytometry.
A D-negative woman has a spontaneous miscarriage at 9 weeks' gestation. Which RhIG dose may be given?
Before 12 weeks, fetal blood volume is small, so a 50 µg microdose is enough (a 300 µg dose is also acceptable). RhIG prevents anti-D formation after early pregnancy loss.
A newborn with Rh HDFN has rising bilirubin despite intensive phototherapy. Intravenous immunoglobulin (IVIG) is given mainly to:
IVIG blocks Fc receptors on macrophages, reducing destruction of antibody-coated red cells, and may lower the need for exchange transfusion.
An infant treated for Rh HDFN is discharged. Three weeks later, hemoglobin is very low with low reticulocytes. The most likely cause is:
Maternal antibody can persist for weeks and continue to destroy red cells, while erythropoiesis is suppressed after transfusions. Infants need hemoglobin monitoring for several weeks.
A pregnant woman has anti-K. Her partner is typed as K-negative, and paternity is certain. What is the risk of HDFN due to anti-K?
If the father is K-negative, the fetus cannot inherit K and is not at risk. Testing the partner's phenotype is a simple first step in assessing risk.
A newborn has severe thrombocytopenia with intracranial bleeding in the first pregnancy. The mother's platelet count is normal. The most likely antibody is:
Fetal and neonatal alloimmune thrombocytopenia is most often due to maternal anti-HPA-1a. Unlike Rh HDFN, it often affects the first pregnancy. A normal maternal count argues against autoimmune ITP.