MLT GlobeMOH exam preparation (UAE) – page 31
700 practice MCQs for the MOH medical laboratory exam. Level: Basic to intermediate.
A technologist has a deep needlestick from an HIV-positive patient. Post-exposure prophylaxis should begin:
HIV PEP is most effective when started as soon as possible, ideally within hours and no later than 72 hours. Waiting for later test results reduces its benefit.
Bleach (sodium hypochlorite) should be stored away from acids mainly because mixing them releases:
Hypochlorite reacts with acids to release toxic chlorine gas. Bleach mixed with ammonia produces chloramine vapours, a different hazard.
An arterial blood gas syringe arrives with a large air bubble that was not expelled. For a patient with pO₂ of 60 mm Hg, the most likely effect is:
Room air has a pO₂ of about 150 mm Hg and almost no CO₂, so gases equilibrate: pO₂ rises toward 150 and pCO₂ falls. Bubbles must be expelled immediately after collection.
A control run fails the 1-3s rule at 11:00. The last acceptable control run was at 07:00. After fixing the problem, the laboratory should:
Patient results since the last acceptable QC may be affected, so they must be reviewed (often by retesting selected samples) and corrected reports issued if needed. Rerunning controls alone does not protect patients.
In a blood smear stained with polychrome methylene blue (M'Fadyean reaction), Bacillus anthracis shows:
The M'Fadyean stain shows the poly-D-glutamic acid capsule of B. anthracis as pink-purple material around blue, square-ended rods. Capsule can also be seen with India ink.
A child has scaly patches of hair loss with 'black dots' where hairs broke at the scalp. Wood's lamp shows no fluorescence, and spores fill the inside of the hair shaft. The most likely dermatophyte is:
T. tonsurans causes endothrix 'black dot' tinea capitis and does not fluoresce. Microsporum canis and M. audouinii are ectothrix and give green fluorescence.
In a hemadsorption test, guinea pig red cells stick to a monkey kidney cell monolayer infected with influenza or parainfluenza virus because:
Infected cells insert viral hemagglutinin into their membranes, and it binds sialic acid on red cells. No antibody is needed for hemadsorption.
Three tubes of bloody CSF are collected. The blood in tube 1 forms a clot on standing. This suggests:
Blood from a traumatic tap contains plasma fibrinogen and can clot, while blood from a subarachnoid haemorrhage has been defibrinated and does not. Clotting is also seen with very high protein, as in spinal block.
A patient with suspected neurosyphilis has a non-reactive CSF VDRL. Which statement is correct?
A reactive CSF VDRL (in a non-bloody sample) is diagnostic, but its sensitivity is limited, so a negative result does not rule out neurosyphilis. VDRL detects non-treponemal (cardiolipin) antibodies.
According to the WHO 2021 manual, what is the lower reference limit (5th centile) for semen volume?
WHO 2021 gives 1.4 mL as the 5th centile of volume in fertile men. Low volume may mean incomplete collection, obstruction or retrograde ejaculation.
According to the WHO 2021 manual, what is the lower reference limit for progressive sperm motility?
The 5th centile is 30% for progressive motility and 42% for total motility (progressive plus non-progressive). 4% is the limit for normal forms.
A semen sample has volume 3.0 mL and sperm concentration 10 × 10⁶/mL. Using WHO 2021 limits, the total sperm number is:
Total number = concentration × volume = 10 × 3.0 = 30 × 10⁶, which is below the WHO 2021 lower limit of 39 × 10⁶ per ejaculate.
Sequential bronchoalveolar lavage aliquots become more bloody, and many macrophages stain positive with Prussian blue. This suggests:
Increasing blood in serial aliquots with haemosiderin-laden macrophages indicates bleeding within the alveoli. Alveolar proteinosis gives milky fluid with PAS-positive material.
For the most sensitive detection of increased urine urobilinogen, a specimen is ideally collected:
Urobilinogen excretion peaks in the early afternoon, linked to the post-meal alkaline tide. First morning urine is best for nitrite and concentrated elements, not urobilinogen.
Small colourless dumbbell-shaped crystals in alkaline urine produce gas bubbles when acetic acid is added. They are:
Calcium carbonate crystals release CO2 (effervescence) in acetic acid. Calcium oxalate monohydrate may also be dumbbell-shaped but does not dissolve or bubble in acetic acid.
In a dilute hypotonic urine, neutrophils swell and their granules show Brownian movement. These cells are called:
Glitter cells are swollen neutrophils in hypotonic urine whose granules sparkle as they move; they stain pale with Sternheimer-Malbin. They have no special diagnostic meaning.
For a standardised sediment, 12 mL of urine is centrifuged, and the supernatant is removed leaving 0.5 mL to resuspend the sediment. The concentration factor is:
The concentration factor is 12 mL ÷ 0.5 mL = 24. Standardising volumes makes results comparable between specimens and laboratories.
The first and rate-limiting enzyme of heme synthesis, ALA synthase, needs which vitamin-derived cofactor?
ALA synthase uses pyridoxal phosphate. This is why some sideroblastic anemias respond to pyridoxine.
Myeloperoxidase in neutrophils is found in which granules?
Myeloperoxidase is a marker enzyme of the primary (azurophilic) granules, which first appear at the promyelocyte stage.
In D typing with a high-protein anti-D reagent, the Rh control tube shows agglutination. The D result is:
A positive control means something other than anti-D (for example IgG-coated cells or rouleaux) is causing agglutination, so the D result cannot be interpreted.