MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 2
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
Which genotypes are possible for a person who types as group A?
The A allele is dominant over O, so group A may be AA or AO. Routine serology cannot tell them apart; molecular testing or family studies are needed.
Reagent red cells used for the routine antibody screen are group:
Group O cells lack A and B antigens, so the patient's anti-A or anti-B cannot react and unexpected antibodies can be detected. A1 and B cells are used for ABO reverse typing.
During panel interpretation, a specificity is usually 'ruled out' when:
If a cell with the antigen (preferably homozygous) does not react, the antibody is unlikely to have that specificity. Using double-dose cells avoids missing weak antibodies with dosage.
Why is an autocontrol tested along with an antibody identification panel?
A positive autocontrol shows antibody or complement on the patient's own cells, pointing to an autoantibody, drug effect or recent transfusion reaction. A negative autocontrol with panel reactivity suggests alloantibody.
Low-ionic-strength saline (LISS) is used in the IAT mainly because it:
Lowering the ionic strength reduces the shielding cloud of ions, so antibody binds faster and incubation can be shortened to 10–15 minutes. AHG is still needed to detect IgG.
After a panel suggests anti-E, some specificities are still not excluded. The next step is usually to:
Selected cells lacking E but carrying the unexcluded antigens show whether another antibody is hiding. Repeating the same panel gives no new information.
Whole blood collected in CPD anticoagulant has a shelf life at 1–6 °C of:
CPD and CP2D support whole blood and red cells for 21 days. Adding adenine (CPDA-1) extends this to 35 days.
Citrate in anticoagulant-preservative solutions prevents clotting by:
Citrate chelates calcium, which is needed for several coagulation steps. Heparin, not citrate, acts through antithrombin.
Massive transfusion in an adult is commonly defined as:
Massive transfusion is replacement of about one total blood volume (roughly 10 or more red cell units in an adult) within 24 hours.
What is the minimum body weight for a donor to give a standard whole blood donation of about 500 mL?
A standard 450–500 mL collection is limited to donors weighing at least 50 kg (110 lb). Lighter donors need a reduced-volume collection with less anticoagulant.
A prospective whole blood donor has an oral temperature of 37.9 °C (100.2 °F). What is the correct action?
Donor temperature must be 37.5 °C (99.5 °F) or lower. A higher value may mean infection, so the donor is deferred; masking fever with an antipyretic is not acceptable.
What is the main benefit of adding nucleic acid testing (NAT) for HIV and HCV to antibody screening of donors?
NAT detects viral RNA days to weeks before antibody appears, so it closes much of the window period. It is not a confirmatory test for antibody results and does not detect bacteria.
A regular donor now tests positive for HIV. Tracing and notifying recipients of his earlier donations is called:
Lookback identifies prior components from a donor who later tests positive, so those units can be retrieved and recipients notified. Reentry is the process of requalifying a donor after a false-positive result.
Which blood pressure is acceptable for an allogeneic whole blood donor?
Donors must have systolic pressure of 180 mmHg or less and diastolic pressure of 100 mmHg or less. Only 175/95 meets both limits.
A D-negative woman without anti-D delivers a baby whose cord cells type D-negative, including a weak D test. What should be done?
RhIG prevents immunization by D-positive fetal cells. If the infant is D-negative, there is no D exposure, so RhIG is not indicated.
Treating red cells with dithiothreitol (DTT) destroys antigens of which blood group system?
Kell antigens depend on disulfide bonds in the Kell glycoprotein, which DTT reduces. Kidd antigens are resistant to DTT and are actually enhanced by proteolytic enzymes.
Anti-Fya is best described as:
Anti-Fya is an immune IgG antibody detected by the indirect antiglobulin test and can cause hemolytic transfusion reactions and mild HDFN. Ficin destroys Fya, so reactions are lost, not enhanced.
A healthy newborn's red cells usually type as:
Lewis antigens are poorly developed at birth, so most cord cells type Le(a−b−). The adult phenotype develops over the first years of life.
Compared with adult red cells, umbilical cord red cells are rich in:
Cord cells carry mainly linear chains (i antigen); branching into I occurs over about 18 months. Adults are therefore I-positive with very little i.
Anti-S is typically:
Anti-S and anti-s are usually IgG, react at the antiglobulin phase and can cause transfusion reactions and HDFN. This contrasts with anti-M and anti-N, which are usually cold IgM.