MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 30
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
Which finding defines neutrophil hypersegmentation on a blood smear?
Hypersegmentation (≥5% with five lobes or any six-lobed cell) is an early sign of megaloblastic anemia from B12 or folate deficiency. Two round joined lobes describe Pelger-Huët cells.
A marrow smear from a patient with fever and massive splenomegaly shows macrophages packed with tiny oval bodies, each with a nucleus and a rod-shaped kinetoplast. These are:
The kinetoplast next to the nucleus identifies Leishmania amastigotes (Leishman-Donovan bodies) of visceral leishmaniasis. Histoplasma yeasts lack a kinetoplast.
Under the 2014 Bethesda System, benign-appearing endometrial cells in a cervical sample are reported when the woman is aged:
Bethesda 2014 raised the reporting age to 45, because endometrial cells in women 45 or older may, rarely, signal endometrial disease. In younger women they are usually normal.
Osmium tetroxide is used as a secondary fixative in electron microscopy mainly because it:
Osmium tetroxide reacts with unsaturated lipids, fixing membranes and adding contrast (it turns black). It penetrates poorly, which is why glutaraldehyde is used first.
For breast carcinoma specimens tested for ER, PR and HER2, ASCO/CAP guidelines recommend fixation in 10% neutral buffered formalin for:
Under-fixation (less than 6 hours) and over-fixation (more than 72 hours) can both give false results for hormone receptors and HER2. The fixation time should be recorded.
Applying vacuum during paraffin infiltration mainly:
Reduced pressure draws out air bubbles and volatile clearing agent, so paraffin enters dense or fatty tissue faster and more completely. It does not change the wax melting point.
In an indirect immunofluorescence test using the flagellate Crithidia luciliae, fluorescence of the kinetoplast indicates antibodies to:
The kinetoplast of Crithidia luciliae contains circular double-stranded DNA free of histones, so its staining is highly specific for anti-dsDNA. Anti-histone antibodies would not stain it because no histones are present.
A 50-year-old man has chronic sinusitis, lung nodules and glomerulonephritis. Neutrophil IIF shows diffuse granular cytoplasmic staining (c-ANCA). The target antigen and likely diagnosis are:
The c-ANCA pattern corresponds mainly to anti-PR3, which is strongly associated with granulomatosis with polyangiitis (upper airway, lung, kidney). MPO antibodies give a p-ANCA pattern and suggest microscopic polyangiitis.
In suspected pernicious anaemia, which autoantibody is the most specific for the diagnosis?
Anti-intrinsic factor antibody is highly specific for pernicious anaemia, though only moderately sensitive. Anti-parietal cell antibody is more sensitive but less specific, being found in atrophic gastritis and some healthy older adults.
A HEp-2 ANA shows bright staining of the nucleoli with little nucleoplasm staining. This pattern is most associated with:
A nucleolar ANA pattern (e.g., anti-PM/Scl, anti-fibrillarin, anti-Th/To) is typical of systemic sclerosis. Drug-induced lupus usually shows a homogeneous pattern from anti-histone antibodies.
A child with suspected celiac disease has selective IgA deficiency. Which serologic test is most appropriate?
IgA-based tests are falsely negative in IgA deficiency, so IgG tests such as IgG anti-DGP (or IgG anti-tTG) are used. IgA anti-endomysial antibody would also be falsely negative.
An elderly patient has tense skin blisters. Direct immunofluorescence of perilesional skin shows linear IgG and C3 along the basement membrane zone. The most likely diagnosis is:
Bullous pemphigoid has autoantibodies to hemidesmosome proteins (BP180, BP230), giving linear basement membrane staining. Pemphigus vulgaris shows intercellular 'fishnet' staining from anti-desmoglein antibodies.
A patient has fatigable ptosis and weakness typical of myasthenia gravis, but acetylcholine receptor antibodies are negative. Which antibody should be tested next?
About a third to half of AChR-negative generalised myasthenia gravis cases have anti-MuSK antibodies. Voltage-gated calcium channel antibodies indicate Lambert-Eaton myasthenic syndrome, which often improves with repeated effort.
A virus reduces MHC class I expression on infected cells so that cytotoxic T cells cannot recognise them. Which cell is best able to kill these infected cells?
NK cells are inhibited by self MHC class I; when class I is lost ('missing self'), the inhibition is removed and the NK cell kills. Plasma cells secrete antibody but do not kill cells directly.
NK cells perform antibody-dependent cellular cytotoxicity (ADCC) against IgG-coated target cells by using which receptor?
CD16 is a low-affinity Fc receptor for IgG; binding IgG on a target cell triggers NK degranulation. CD21 and CD35 are complement receptors, not Fc receptors.
The main action of type I interferons (IFN-α and IFN-β) is to:
Virus-infected cells release IFN-α/β, which induce nearby cells to make proteins that block viral replication and increase MHC class I. IgE switching is driven by IL-4.
Which pair of cytokines is mainly anti-inflammatory and immunosuppressive?
IL-10 and TGF-β inhibit macrophage activation and T-cell proliferation and are produced by regulatory T cells. IL-1 and TNF-α are classic pro-inflammatory cytokines.
A student has infectious mononucleosis. Epstein–Barr virus enters B lymphocytes by binding which molecule?
EBV glycoprotein gp350 binds CD21 (CR2), the receptor for C3d, on B cells. CD4 is the main receptor for HIV.
During T-cell development, positive selection in the thymic cortex ensures that surviving thymocytes:
Only thymocytes whose TCR binds self-MHC weakly receive survival signals, giving MHC restriction. Removal of strongly self-reactive cells is negative selection.
Thymocytes that express both CD4 and CD8 on their surface are:
Thymocytes progress from double-negative to double-positive (CD4+CD8+) in the cortex, then become single-positive cells after selection. Mature blood T cells are normally single-positive.