MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 34
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
A woman has Raynaud phenomenon, calcinosis, sclerodactyly and telangiectasia. Which autoantibody is most likely positive?
These features describe limited cutaneous systemic sclerosis (CREST syndrome), which is strongly associated with anti-centromere antibodies.
Before a kidney transplant, the recipient's serum gives a positive crossmatch against donor T lymphocytes. What does this usually mean?
A positive T-cell crossmatch shows preformed antibodies against donor HLA, which can cause hyperacute or acute antibody-mediated rejection, so the transplant is usually not performed.
In typhoid fever, agglutinating antibodies detected by the Widal test usually reach diagnostic (rising) titres from which stage of illness?
Widal antibodies begin to appear at the end of the first week and rise to diagnostic titres in the second week, which is why blood culture is preferred in the first week.
Epidemic cholera is caused mainly by Vibrio cholerae of which serogroups?
Only toxigenic O1 and O139 strains cause epidemic cholera; O157 is a serogroup of E. coli.
Which Neisseria meningitidis serogroup has historically caused the large epidemics of the African 'meningitis belt'?
Serogroup A caused the major meningitis-belt epidemics, which fell sharply after mass conjugate vaccination.
In a GasPak anaerobic jar, what is the role of the palladium catalyst?
The generating envelope releases hydrogen and CO2; palladium catalyses the reaction of hydrogen with residual oxygen to form water.
A small lemon-shaped cyst with a single nucleus and a knob-like projection at one end is seen in stool. It belongs to a non-pathogenic flagellate called:
The lemon-shaped cyst with an anterior nipple is characteristic of the commensal flagellate Chilomastix mesnili.
Patients with Strongyloides stercoralis infection are at greatest risk of life-threatening hyperinfection when they receive:
Corticosteroids and other immunosuppression allow massive autoinfection and dissemination of larvae.
How do schistosomes differ from most other human flukes?
Schistosomes are dioecious, with the female held in the male's gynaecophoric canal; most other trematodes are hermaphrodites.
For zinc sulphate flotation concentration of stool, the zinc sulphate solution is adjusted to a specific gravity of about:
At about 1.18 (1.20 for formalin-fixed stool), cysts and light eggs float while most debris sinks.
On CHROMagar Candida, Candida albicans typically forms colonies that are:
The chromogenic medium gives green C. albicans colonies; C. tropicalis is blue and C. krusei pink and rough.
The HIV virion contains which genetic material?
Retroviruses are diploid, carrying two identical positive-sense RNA strands that are copied into DNA by reverse transcriptase.
To prevent transfusion-transmitted cytomegalovirus in a low-birth-weight neonate, the blood bank supplies red cells that are:
CMV is carried in white cells, so CMV-negative or leucoreduced components reduce transmission; irradiation prevents graft-versus-host disease, not CMV.
Which reagent can dehydrate tissue and also mix directly with paraffin, so a separate clearing step can be skipped?
Dioxane is miscible with water and paraffin, acting as a dehydrant–clearant, though its toxicity limits use; ethanol needs a clearing agent.
A renal biopsy fixed for EM in buffered glutaraldehyde is later processed for light microscopy. Which staining problem is most likely?
Glutaraldehyde leaves free aldehyde groups that react with Schiff reagent, giving non-specific PAS positivity. Morphology is otherwise very well preserved.
Which plant lectin is used as a reagent to detect the B antigen?
Griffonia (Bandeiraea) simplicifolia lectin reacts with B antigen. Dolichos biflorus detects A1, Ulex europaeus detects H, and Arachis hypogaea detects T antigen.
ZZAP reagent, used to prepare cells for adsorption, contains:
ZZAP combines DTT with papain or ficin. It removes bound IgG and makes cells adsorb better, but it destroys Kell, Duffy, MNS and other sensitive antigens.
Red cells collected in CPDA-1 without an additive solution must have a hematocrit no higher than:
Packed CPDA-1 red cells must have a hematocrit ≤ 80% so that enough glucose remains in the small plasma volume for 35 days.
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 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.