MLT GlobeDOH exam preparation (Abu Dhabi) – page 33
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
A 1:20 dilution of blood is made using 0.05 mL of blood. How much diluent must be added?
Total volume = 0.05 × 20 = 1.0 mL, so diluent = 1.0 − 0.05 = 0.95 mL.
How many grams of sodium chloride (MW 58.5 g/mol) are needed to prepare 500 mL of a 0.1 mol/L solution?
Moles needed = 0.1 × 0.5 = 0.05 mol, and 0.05 × 58.5 = 2.925 g.
Which membrane lipids, abundant in plant chloroplasts, have a sugar joined by a glycosidic bond directly to glycerol?
Galactolipids carry galactose linked directly to C-3 of diacylglycerol. Sphingolipids use a sphingosine backbone, and phosphoglycerides link head groups through phosphate.
α-Oxidation removes one carbon from the carboxyl end of branched fatty acids. Its defect causes accumulation of phytanic acid in:
Phytanic acid's β-methyl group blocks β-oxidation, so α-oxidation (in peroxisomes, notably in nervous tissue) must act first. Tay–Sachs and Gaucher are lysosomal storage diseases; MCAD affects β-oxidation.
Which statement about streptococci and related cocci is INCORRECT?
Most viridans streptococci lack a Lancefield antigen or are non-groupable; they are identified by biochemical tests, MALDI-TOF or sequencing.
A penicillin-non-susceptible Streptococcus pneumoniae is isolated from a patient with pneumonia. Which beta-lactam is usually still effective?
Altered penicillin-binding proteins reduce aminopenicillin activity, but third-generation cephalosporins like ceftriaxone usually remain active; vancomycin is added for meningitis.
A commonly used pleural fluid adenosine deaminase cut-off supporting tuberculous pleurisy is about:
Pleural ADA above roughly 40 U/L, in a lymphocytic exudate, strongly supports tuberculosis in high-prevalence settings. Serum ADA reference ranges vary by method.
When Ziehl–Neelsen staining for Mycobacterium leprae, the usual decolouriser is:
M. leprae is less acid-fast than M. tuberculosis, so a weaker decolouriser (5% H2SO4) is used. 20% sulphuric acid is used for M. tuberculosis in some protocols.
Rat-bite fever (sodoku) in Asia, with a short, rigid spiral organism seen by dark-ground microscopy, is caused by:
Spirillum minus causes sodoku and is not a Borrelia. B. duttonii and B. recurrentis cause tick- and louse-borne relapsing fever.
Many viruses encode proteins that block apoptosis. Which virus instead is known to trigger apoptosis of its host cells as a mechanism of damage?
Rubella virus induces apoptosis in infected cells, contributing to fetal damage. Poxviruses (vaccinia, myxoma) and EBV encode anti-apoptotic proteins to prolong cell survival.
Hepatitis D virus is placed in which genus under current taxonomy?
HDV is the type species of genus Deltavirus, now in family Kolmioviridae. HAV is a hepatovirus, HBV an orthohepadnavirus, and HCV a hepacivirus.
Cache Valley virus, an orthobunyavirus causing birth defects in sheep and rare human infection, is transmitted by which vectors?
Cache Valley virus is carried by several mosquito genera, including Aedes, Anopheles and Culiseta. Ticks, sandflies and fleas are not its vectors.
Gram stain of pus from a brain abscess shows beaded, branching Gram-positive filaments that are partially acid-fast with modified Kinyoun stain. Which aerobic actinomycete is likely?
Nocardia is an aerobic branching actinomycete that is partially acid-fast and spreads from lung to brain. Actinomyces is anaerobic and not acid-fast; Streptomyces is non-acid-fast; M. tuberculosis does not branch.
Which Babesia species is known for causing severe, often fatal infection in splenectomized people in Europe?
B. divergens, a cattle parasite, causes fulminant hemolytic disease mainly in asplenic patients in Europe. B. microti causes milder disease in the USA.
Which statement correctly describes reverse T3 (rT3)?
Inner-ring deiodination of T4 in tissues yields inactive rT3. In non-thyroidal (euthyroid sick) illness rT3 rises because its clearance falls, not decreases.
A group A patient with colon cancer suddenly types as AB with a weak anti-B reaction, while the plasma still contains anti-B. The most likely explanation is:
Bacterial deacetylase (in colon cancer, obstruction or gram-negative sepsis) turns N-acetylgalactosamine, the A sugar, into galactosamine, which resembles the B sugar and reacts with some anti-B reagents. The patient's own anti-B does not react with his cells.
A group A1 patient's cold antibody reacts strongly with group O cells, weakly with A2 cells and hardly with A1 cells or his own cells. The most likely antibody is:
Anti-IH reacts with cells having the most H and I antigen; group O and A2 cells have much more H than A1 cells. Anti-A1 would react with A1 cells, not O cells.
A group A infant of a group O mother has a positive DAT. The maternal antibody screen is negative, and an eluate from the infant's cells is negative with group O panel cells. What should be done next?
Group O panel cells lack A and B, so anti-A in an eluate will not react with them. Testing the eluate with A1 and B cells shows the IgG anti-A that confirms ABO HDFN.
Women with the rare p phenotype often have an antibody linked to recurrent early miscarriage. This antibody is:
People with the p phenotype lack P1, P and Pk and make anti-PP1Pk, which can attack the placenta, which is rich in P and Pk. Anti-P1 alone is usually a weak cold antibody.
Why can glucose still fall during the first hour after collection in a sodium fluoride tube?
Fluoride inhibits enolase, a late step of glycolysis, and takes 1–4 hours to be fully effective. Placing the tube in ice slurry or using a citrate-buffered tube gives immediate protection.