MLT GlobeQCHP exam preparation (Qatar) – page 3
749 practice MCQs for the QCHP medical laboratory exam. Level: Intermediate.
A trauma patient's ABO discrepancy cannot be resolved and he needs red cells immediately. Which red cells should be issued?
Until the discrepancy is resolved, group O red cells are given because they lack A and B antigens. Group AB red cells would be incompatible with anti-A or anti-B in the plasma.
A group B patient needs red cells, but no group B units are available. Which ABO group of red cells is the best alternative?
A group B patient has anti-A, so red cells must lack A antigen. Group O red cells lack both A and B and are compatible.
For routine tube ABO forward typing, red cells are usually tested as a suspension of what concentration and read after:
Standard tube ABO typing uses a 2–5% saline cell suspension, centrifuged immediately and read for agglutination. ABO IgM antibodies do not need incubation or AHG.
Which test is an application of the indirect antiglobulin test rather than the DAT?
The IAT first sensitizes reagent cells with plasma antibody in vitro, then adds AHG; this is used in antibody screens, crossmatches and antigen typing. The other options test cells already coated in vivo.
After identifying anti-Fya, the patient's own red cells should be typed and are expected to be:
A person cannot normally make an alloantibody to an antigen on his own cells. Finding the patient Fy(a−) supports the identification.
An antibody reacts only at immediate spin, is weak, and all reactive cells are P1-positive. This antibody is:
Anti-P1 is usually a naturally occurring cold IgM that rarely causes hemolysis. Antibodies reacting only below 37 °C are generally not clinically significant.
An antibody titration shows 2+ at 1:32, 1+ at 1:64 and no agglutination at 1:128. The titer is reported as:
The titer is the reciprocal of the highest dilution giving 1+ agglutination, here 1:64. The 1:128 tube is negative and is not counted.
Red cells washed in an open system and stored at 1–6 °C expire after:
Opening the system raises the risk of bacterial contamination, so washed red cells expire 24 hours after washing when refrigerated.
Which intravenous fluid may be given through the same line as red cells?
Only normal saline is routinely compatible with red cells. Dextrose solutions cause hemolysis and lactated Ringer's contains calcium that can cause clotting.
A group A, D-negative woman aged 25 needs red cells. Which units are the correct choice?
Group A patients have anti-B, so A or O red cells are compatible. D-negative units prevent anti-D formation in a woman of childbearing potential.
A trauma patient of unknown blood group needs plasma immediately. Which plasma group is the universal choice?
AB plasma contains neither anti-A nor anti-B, so it is compatible with every ABO group. Group O plasma contains both antibodies.
After transfusion, the patient's pretransfusion sample and a donor segment must be kept refrigerated for at least:
Keeping both samples for at least 7 days allows re-testing if a delayed or acute reaction is investigated.
An autologous unit was not needed during surgery. What should be done with it?
Autologous donors do not meet all allogeneic donor criteria, so unused units are not crossed over for other patients. They are discarded after expiry or when no longer needed.
A woman with anti-D has a partner who is D-positive and heterozygous for RHD. What is the chance that each fetus is D-positive?
A heterozygous (D/d) father passes the RHD gene to half of his children. A homozygous father would give a D-positive fetus in every pregnancy.
Which tests are routinely performed on cord blood of an infant born to a mother with a clinically significant antibody?
Cord blood ABO, D type and DAT show whether the infant has antigen-positive cells coated with maternal antibody. Reverse grouping is not useful in newborns.
Why is ABO typing of a newborn usually limited to forward (cell) grouping?
Infants do not form their own ABO antibodies until about 3–6 months; any present came from the mother. Reverse grouping would give misleading results.
What are the main goals of exchange transfusion in a newborn with severe HDFN?
Exchange removes unconjugated bilirubin, sensitized red cells and free maternal antibody, while giving antigen-negative red cells to correct anemia.
Phototherapy lowers bilirubin in newborns with HDFN by:
Blue light changes unconjugated bilirubin into photoisomers that are excreted in bile and urine without conjugation. It does not affect maternal antibody.
Apart from D, which red cell antigen is the most likely to cause alloimmunization after transfusion?
K is highly immunogenic, second only to D among non-ABO antigens. Many transfusion services therefore give K-negative red cells to girls and women of childbearing age.
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.