MLT GlobeMOH exam preparation (UAE) – page 35
700 practice MCQs for the MOH medical laboratory exam. Level: Basic to intermediate.
In intravascular hemolysis, once haptoglobin is saturated, free heme released from hemoglobin is carried mainly by:
Hemopexin binds free heme and carries it to the liver, so it falls in severe intravascular hemolysis. Transferrin carries free ferric iron, not heme, and ferritin is a storage protein.
A child of consanguineous parents has microcytic anemia that does not respond to oral iron. Transferrin saturation is very low and hepcidin is inappropriately normal to high. Which gene defect is most likely?
TMPRSS6 encodes matriptase-2, which normally suppresses hepcidin. Its loss keeps hepcidin high and blocks iron absorption (iron-refractory iron deficiency anemia). HFE mutations cause low hepcidin and iron overload.
An older man has marked splenomegaly and lymphocytes with short hair-like projections at one pole of the cell. Cells are CD19+, CD5−, CD103−, CD25−. The most likely diagnosis is:
'Villous' lymphocytes with polar projections and a CD5−/CD103− B-cell phenotype fit splenic marginal zone lymphoma. Classic hairy cell leukemia has circumferential projections and is CD103+, CD25+, CD11c+.
A cell in the monocyte series has a large, folded nucleus with fine chromatin and one or two nucleoli, and grey-blue cytoplasm with fine azurophilic granules. It is a:
Promonocytes show nuclear folding with fine chromatin and nucleoli, and are counted as blast equivalents in AML with monocytic differentiation. Mature monocytes lack visible nucleoli.
Before starting abacavir for HIV, the laboratory is asked to test for which allele to prevent a serious hypersensitivity reaction?
HLA-B*57:01 carriers have a high risk of abacavir hypersensitivity, so screening is recommended before treatment. HLA-B27 relates to spondyloarthritis, not drug reactions.
In adults, antibodies against bacterial capsular polysaccharides, such as pneumococcal capsule, are mainly of which IgG subclass?
Polysaccharide antigens mostly induce IgG2, so IgG2 deficiency predisposes to encapsulated bacterial infections. Protein antigens mainly induce IgG1 and IgG3.
In the differential absorption (Davidsohn) test, the heterophile antibody of infectious mononucleosis is:
The infectious mononucleosis heterophile antibody is not a Forssman antibody, so it is not removed by guinea pig kidney but is removed by beef red cells. Forssman antibodies are removed by guinea pig kidney.
After allogeneic stem cell transplantation, donor engraftment is best monitored in the laboratory by:
STR analysis compares donor- and recipient-specific DNA markers in blood or marrow to measure the percentage of donor cells. ABO typing may not change if donor and recipient share the same group.
A 5-year-old with an unsteady gait and small dilated vessels on the conjunctivae has recurrent sinopulmonary infections and IgA deficiency. Which serum test is typically raised?
Ataxia-telangiectasia (ATM gene) shows ataxia, telangiectasia, IgA/IgG2 deficiency and a characteristically raised serum AFP. IgE is usually low or normal in this disorder.
A patient on peritoneal dialysis with icodextrin has high glucose meter readings but a normal plasma glucose on the laboratory analyser. Which meter enzyme is most likely used?
GDH-PQQ also reacts with maltose, which is formed from icodextrin, giving falsely high readings. Glucose oxidase meters are specific for glucose and not affected by maltose.
A procedure requires 1000 × g. The centrifuge rotor radius is 15 cm. Using RCF = 1.118 × 10⁻⁵ × r × rpm², the required speed is about:
rpm = √[1000 ÷ (1.118 × 10⁻⁵ × 15)] = √(1000 ÷ 0.0001677) = √5,963,000 ≈ 2440 rpm. The value 5960 comes from not taking the square root correctly.
An epidemiological cutoff value (ECV) for an organism-drug pair is used to:
The ECV is the highest MIC of the wild-type population; isolates above it are 'non-wild type'. Unlike clinical breakpoints, ECVs do not predict treatment outcome.
A dog bite wound grows a catalase-positive coccus in clusters. It is tube coagulase positive, PYR positive and Voges-Proskauer negative. The most likely organism is:
S. pseudintermedius, a canine commensal, is coagulase positive but PYR positive and VP negative. S. aureus is usually PYR negative and VP positive; S. lugdunensis and S. epidermidis are tube coagulase negative.
A Mycobacterium abscessus isolate has a clarithromycin MIC in the susceptible range on day 3. CLSI recommends reading clarithromycin again at day 14 because:
Many M. abscessus strains carry a functional erm(41) gene that induces macrolide resistance during exposure, visible only with extended incubation. The organism itself grows in 3–5 days.
Before plating sputum on BCYE agar for Legionella, a brief acid treatment (pH about 2.2) may be used. Its purpose is to:
Legionella tolerates short exposure to acid better than most respiratory flora, so acid pretreatment reduces overgrowth by contaminants. Selective BCYE with antibiotics serves the same aim.
During imipenem therapy, a Pseudomonas aeruginosa becomes imipenem resistant but stays susceptible to ceftazidime and cefepime, and carbapenemase tests are negative. The most likely mechanism is:
Imipenem enters P. aeruginosa mainly through the OprD porin. Loss of OprD causes imipenem resistance without affecting cephalosporins, and carbapenemase tests stay negative.
Which set of specimens is used for ante-mortem laboratory diagnosis of human rabies?
No single ante-mortem test is sensitive, so saliva and skin biopsy (RT-PCR, antigen detection) are tested with serum and CSF antibodies. Brain tissue is used after death.
A CSF cytospin from a patient with a ventricular shunt shows tight clusters of cells with round nuclei and abundant cytoplasm, looking uniform. They most likely are:
Choroid plexus and ependymal cells can appear in clusters after shunts or neurosurgery and have uniform nuclei. They must not be mistaken for malignant cells, which show pleomorphism.
Bronchoalveolar lavage from a patient with hilar lymphadenopathy shows 35% lymphocytes with a CD4:CD8 ratio of 5. This most suggests:
Lymphocytosis with a CD4:CD8 ratio above 3.5 strongly supports sarcoidosis. Hypersensitivity pneumonitis also causes lymphocytosis but usually with a low CD4:CD8 ratio.
A patient with acute abdominal pain and confusion has a strongly positive urine Ehrlich reaction. Which test distinguishes porphobilinogen from urobilinogen?
Ehrlich's reagent reacts with both urobilinogen and porphobilinogen; the Watson-Schwartz test uses solvent extraction to tell them apart, and the Hoesch test is a rapid PBG screen. Acetest detects ketones.