MLT GlobeBlood Banking: HDFN – page 3
56 Blood Banking MCQs on HDFN with answers and explanations.
Hydrops fetalis in severe HDFN results mainly from:
Severe fetal anemia causes high-output heart failure, and extramedullary hematopoiesis in the liver reduces protein synthesis. Together these cause generalized edema.
Bilirubin rises quickly after birth in HDFN mainly because:
Before birth the placenta clears bilirubin to the mother. After birth the immature liver has little glucuronyl transferase activity, so bilirubin from ongoing hemolysis builds up.
Rh immune globulin is thought to prevent anti-D formation mainly by:
Passive anti-D coats fetal D-positive cells that entered the mother's blood, leading to their removal before she makes her own anti-D. The exact mechanism is not fully proven, but antigen clearance is the accepted textbook explanation.
In the Kleihauer-Betke acid-elution test, fetal red cells appear:
HbF resists acid elution and stays in the fetal cells, which stain with eosin. Adult HbA is washed out, leaving pale ghost cells.
A pregnant woman's anti-D titer was 8 at 20 weeks. The frozen earlier sample is tested in parallel with a new sample at 24 weeks. Which new titer indicates a significant rise?
Titration has an error of about one dilution, so only a rise of two or more dilutions (fourfold, e.g. 8 to 32) is significant. A change from 8 to 16 may be technical variation.
In ABO HDFN, why is the infant's DAT often only weakly positive?
A and B antigens are not fully developed at birth, so less antibody binds each cell. Much maternal IgG anti-A,B is also absorbed by A/B substances in fetal tissues and fluids.
A double-volume exchange transfusion in a newborn removes approximately what fraction of the infant's original red cells?
Because incoming and outgoing blood mix, a double-volume exchange replaces about 85–90% of the infant's red cells. It removes only about half of the total bilirubin because of extravascular bilirubin.
A 3 kg term infant needs a double-volume exchange transfusion. Using a blood volume of 85 mL/kg, what volume is needed?
Blood volume = 3 × 85 = 255 mL. A double-volume exchange uses twice this, 510 mL.
A D-negative mother with sickle cell disease has a high fetal cell count by Kleihauer-Betke. Which method best confirms the fetal bleed?
Maternal F cells (raised HbF) resist acid elution and falsely raise KB counts. Flow cytometry separates fetal cells, which are HbF-positive and carbonic anhydrase-negative, from adult F cells.
A postpartum rosette test is strongly positive with many rosettes. The mother was later found to be weak D positive. The best explanation is:
The rosette test detects D-positive cells in a D-negative mother. If the mother's cells express weak D, they bind anti-D and form rosettes; a quantitative test such as flow cytometry is needed.
A group A infant of a group O mother has a positive DAT. The maternal antibody screen is negative, and an eluate from the infant's cells is negative with group O panel cells. What should be done next?
Group O panel cells lack A and B, so anti-A in an eluate will not react with them. Testing the eluate with A1 and B cells shows the IgG anti-A that confirms ABO HDFN.
A Kleihauer-Betke test shows 30 fetal cells in 2000 cells counted. Using 5000 mL maternal blood volume, how many 300 µg RhIG vials are needed?
30/2000 = 1.5%. Fetal bleed = 1.5 × 50 = 75 mL whole blood. 75 ÷ 30 = 2.5, rounded up to 3, then add 1 vial = 4 vials.
Why can anti-K cause severe fetal anemia with relatively little rise in amniotic fluid bilirubin?
Kell antigens appear on early erythroid progenitors, so anti-K suppresses red cell production as well as causing hemolysis. Bilirubin and titers therefore underestimate the anemia.
A pregnant woman is found to have partial D category DVI. How should she be managed for RhIG?
People with partial D, such as DVI, lack parts of the D antigen and can make anti-D. Pregnant women with partial D should receive RhIG and D-negative red cells.
In a jaundiced newborn with HDFN, why are drugs such as sulfonamides avoided?
Only unbound unconjugated bilirubin crosses the blood-brain barrier. Drugs that displace bilirubin from albumin raise free bilirubin and the risk of kernicterus.
A newborn of a mother with high-titer anti-D types D-negative, but the DAT is strongly positive with IgG. The most likely explanation is:
In 'blocked D', heavy coating with maternal anti-D leaves no free sites for the typing reagent, causing a false D-negative type. An eluate showing anti-D or a monoclonal IgM test can confirm.