MLT GlobeMOH exam preparation (UAE) – page 30
700 practice MCQs for the MOH medical laboratory exam. Level: Basic to intermediate.
A febrile patient with recurring fever episodes has long, loosely coiled spiral organisms lying between red cells on a Wright-stained smear. The most likely organism is:
Relapsing fever Borrelia are large enough to be seen on routine stained smears during fever spikes. T. pallidum and Leptospira are too thin for routine smears, and Bartonella appears as small rods on red cells.
Stomatocytes due to an acquired cause are most often associated with:
Acquired stomatocytosis is classically linked to acute or chronic alcohol excess and liver disease. The other conditions are associated with pencil cells, basophilic stippling and macro-ovalocytes.
AML blasts with cup-shaped nuclear invaginations, normal karyotype and aberrant cytoplasmic nucleophosmin are found. Without FLT3-ITD, this mutation is linked to:
NPM1-mutated AML is the most common AML with a normal karyotype and, without FLT3-ITD, has a favorable prognosis. It is a defining genetic abnormality in WHO 5th edition.
A child has lytic skull lesions. Biopsy shows cells with grooved nuclei positive for CD1a and langerin (CD207). The diagnosis is:
Langerhans cells are CD1a+, S100+ and langerin+, with Birbeck granules; many cases carry BRAF V600E. Myeloma causes lytic lesions but is rare in children and shows plasma cells.
A febrile child has pancytopenia, splenomegaly, ferritin above 10 000 µg/L, high triglycerides, low fibrinogen and marrow macrophages engulfing blood cells. The likely diagnosis is:
HLH is uncontrolled macrophage/T-cell activation with fever, cytopenias, very high ferritin, hypertriglyceridemia, low fibrinogen and hemophagocytosis; soluble CD25 is also high. Transfusion iron overload does not cause fever and hemophagocytosis.
Naphthol AS-D chloroacetate esterase (specific esterase) is positive mainly in:
Chloroacetate esterase marks neutrophil lineage cells and mast cells. Monocytic cells are shown by non-specific (alpha-naphthyl) esterase, which is fluoride-inhibited.
A patient with recurrent venous thrombosis has a prolonged aPTT that does not correct on mixing with normal plasma and a positive dilute Russell viper venom time. Why is the aPTT prolonged in vitro?
Lupus anticoagulants bind phospholipid-protein complexes and prolong phospholipid-dependent tests in vitro, yet cause thrombosis in vivo. Factor VIII deficiency would correct on mixing and causes bleeding, not thrombosis.
Cytotoxic T lymphocytes kill virus-infected target cells mainly by releasing:
Perforin forms pores in the target membrane and granzymes enter to trigger apoptosis. Major basic protein is an eosinophil product used against helminths.
During the neutrophil respiratory burst, which enzyme complex produces superoxide from molecular oxygen?
NADPH oxidase reduces oxygen to superoxide, which is converted to hydrogen peroxide. Myeloperoxidase then uses hydrogen peroxide to make hypochlorite; it does not make superoxide.
Differentiation of a naive CD4 T cell into a Th1 cell is mainly driven by which cytokine from dendritic cells and macrophages?
IL-12 induces T-bet and IFN-γ production, leading to Th1 cells that activate macrophages. IL-4 drives Th2 differentiation instead.
Besides TCR binding to peptide–MHC, full activation of a naive T cell requires a costimulatory signal between:
CD28 binding B7 molecules on activated antigen-presenting cells provides 'signal 2'. CD8 binds MHC class I, not class II.
For a B cell to switch from IgM to IgG production in response to a protein antigen, helper T cells must engage the B cell through:
CD40L on activated helper T cells binding CD40 on B cells, together with cytokines, drives class switching and germinal-centre formation. Absence of CD40L causes hyper-IgM syndrome.
Germinal centres, where B cells proliferate and undergo selection, are found in:
Antigen stimulation turns primary follicles into secondary follicles with germinal centres. Primary follicles contain resting naive B cells without germinal centres.
Peptides from viral proteins made in the cytosol are carried into the endoplasmic reticulum for loading onto MHC class I by:
Proteasome-generated peptides are pumped into the ER by TAP1/TAP2 and loaded onto class I molecules. The invariant chain and HLA-DM belong to the class II pathway.
A patient needs a stem cell donor. Assuming no recombination, what is the chance that one full sibling is HLA-identical to the patient?
HLA genes are inherited as two parental haplotypes; a sibling has a 1 in 4 chance of receiving the same two haplotypes. 50% is the chance of sharing exactly one haplotype.
Serum for classical complement studies was accidentally collected in an EDTA tube. Classical pathway activity will be absent mainly because EDTA:
C1q, C1r and C1s need Ca²⁺ to stay assembled; the alternative pathway needs Mg²⁺, which EDTA also removes. Serum, not EDTA plasma, is the specimen for functional complement tests.
A healthcare worker completed hepatitis B vaccination and has never been infected. Which serological profile is expected?
The recombinant vaccine contains only HBsAg, so it produces anti-HBs alone. Anti-HBc appears only after natural infection.
A seronegative stem cell recipient needs transfusion. Which component attribute best reduces the risk of transfusion-transmitted cytomegalovirus?
CMV lives in donor leukocytes, so leukoreduction or use of CMV-seronegative donors reduces transmission. Irradiation prevents TA-GVHD but does not remove CMV.
The main advantage of a double-beam spectrophotometer over a single-beam instrument is that it:
By splitting light between sample and reference paths and comparing them, a double-beam instrument cancels variations in source intensity. It still needs a monochromator and appropriate blanks.
A serum potassium is 4.0 mEq/L. Potassium has an atomic weight of 39 and a valence of 1. What is the result in mg/dL?
For a monovalent ion, 4.0 mEq/L = 4.0 mmol/L × 39 mg/mmol = 156 mg/L = 15.6 mg/dL. Reporting mg/L as mg/dL gives 156.