MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 10
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
A smear from an adult with homozygous sickle cell disease in steady state is most likely to show:
HbSS smears show irreversibly sickled cells and target cells, and Howell-Jolly bodies appear after autosplenectomy. Pencil cells suggest iron deficiency, and macro-ovalocytes suggest megaloblastic anemia.
The biconcave shape of a normal red cell mainly allows it to:
A biconcave disc has more surface area than a sphere of the same volume, so it can fold and pass through narrow capillaries and splenic slits. Spherocytes lose this reserve and are trapped.
A CLL patient develops a falling hemoglobin, spherocytes, raised bilirubin and reticulocytosis. The most useful next test is:
Warm autoimmune hemolytic anemia is a common complication of CLL; a positive DAT confirms immune hemolysis. Osmotic fragility shows spherocytes but does not separate immune from hereditary causes.
The most common non-Hodgkin lymphoma in adults worldwide is:
Diffuse large B-cell lymphoma accounts for about one-third of adult NHL. Follicular lymphoma is the most common indolent type but is less frequent overall.
In primary myelofibrosis, the degree of marrow fibrosis is graded using which stain?
Reticulin fibers are shown by silver stains and graded MF-0 to MF-3; trichrome shows collagen. Perls stain shows iron stores and ring sideroblasts.
The large orange-red granules of eosinophils contain a toxic protein that damages helminths. It is:
Eosinophil specific granules contain major basic protein, eosinophil cationic protein and eosinophil peroxidase. Histamine is mainly stored in basophil and mast cell granules.
A patient with advanced HIV infection is most likely to show which lymphocyte result by flow cytometry?
HIV destroys CD4+ T helper cells, so the CD4 count falls and the CD4:CD8 ratio (normally about 1–3) is reversed. Absolute CD4 counts guide staging and prophylaxis.
On a 5-part automated differential using flow cytometry, side-scattered light mainly reflects:
Forward scatter relates to cell size, and side scatter to internal structure such as granules and nuclear lobes; eosinophils and neutrophils have high side scatter. Antigens need labeled antibodies.
A cervical smear shows multinucleated cells with nuclear molding, chromatin pushed to the nuclear edge and a ground-glass appearance. The most likely cause is:
Multinucleation, molding and margination of chromatin (the '3 Ms') are typical of herpes simplex virus infection. HPV produces koilocytes rather than multinucleated molded cells.
Alcohol-based fixatives such as ethanol and methanol act mainly by:
Alcohols remove water and denature (coagulate) proteins without forming cross-links, which can cause shrinkage and hardening. Methylene cross-linking is how formaldehyde works.
The main purpose of the clearing step in paraffin processing is to:
Paraffin does not mix with alcohol, so a clearing agent such as xylene, miscible with both, replaces the alcohol. Water is removed earlier by dehydration in graded alcohols.
Small tubular structures such as a vas deferens or fallopian tube are best embedded:
Embedding tubes on end gives transverse sections showing the lumen and all wall layers. Longitudinal orientation may miss the lumen or show only part of the wall.
Positively charged or silane-coated slides are used for immunohistochemistry mainly to:
Harsh steps such as heating in retrieval buffer can detach sections, and charged or coated slides hold them firmly. Endogenous peroxidase is blocked with hydrogen peroxide, not by the slide type.
Tissue cassettes should be labeled with pencil or solvent-resistant ink mainly because:
Alcohols and xylene during processing can dissolve normal ink, risking loss of specimen identity. Pencil, solvent-resistant markers or printed labels keep the identification.
A jeweller develops an itchy eczematous rash where a nickel bracelet touches her skin. A patch test is read at 48–96 hours. The mechanism is:
Allergic contact dermatitis is delayed-type (type IV) hypersensitivity: sensitised T cells react to hapten-protein complexes over 48–96 hours. IgE-mediated reactions appear within minutes.
Which method is considered the reference screening method for antinuclear antibodies?
Indirect immunofluorescence on HEp-2 cells detects a wide range of nuclear and cytoplasmic antibodies and gives pattern information. Immunodiffusion detects only selected ENA specificities and is less sensitive.
In flow cytometry, which marker is expressed on essentially all leukocytes and is used to gate white cells away from red cells and debris?
CD45 (leukocyte common antigen) is present on all nucleated haematopoietic cells, so CD45 versus side scatter is the standard leukocyte gate. CD34 marks only stem/progenitor cells.
Which surface marker is most characteristic of monocytes and macrophages?
CD14, the receptor for LPS-binding protein complexes, is strongly expressed by monocytes. CD19 is a B-cell marker and CD56 is found on NK cells.
A patient with a helminth infection has marked eosinophilia. Which cytokine mainly drives eosinophil production and activation?
IL-5, produced by Th2 cells and ILC2s, stimulates eosinophil growth, differentiation and activation. IL-12 and IFN-γ drive Th1 responses instead.
In adult humans, B lymphocytes develop from progenitors mainly in the:
The bone marrow is the primary lymphoid organ for B-cell development in humans. The thymus is where T cells mature.