MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 5
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
In an immunoprecipitation reaction, antigen excess that leads to small soluble complexes and a false-low result is called:
Postzone is antigen excess; prozone is antibody excess. Maximum lattice formation and precipitation occur at the zone of equivalence.
Indirect immunofluorescence for antibodies differs from direct immunofluorescence because it uses:
In the indirect method, patient antibody binds the substrate antigen and is detected by fluorescein-labelled anti-human immunoglobulin. The direct method applies labelled antibody straight to the tissue antigen.
Compared with the erythrocyte sedimentation rate, CRP as an inflammatory marker:
CRP rises within 6–12 hours of inflammation and falls quickly when it resolves (half-life about 19 hours). ESR changes slowly and is affected by red cell and plasma protein factors.
The most common primary immunodeficiency, which may cause anaphylaxis to transfused blood products if anti-IgA antibodies are present, is:
Selective IgA deficiency is the most common primary immunodeficiency and is often asymptomatic. Some patients make anti-IgA and need IgA-deficient or washed products.
In a modern spectrophotometer, which component most commonly isolates a narrow band of wavelengths from the light source?
A monochromator such as a diffraction grating (or prism) disperses light and selects a narrow band. The photomultiplier tube is the detector, not the wavelength selector.
How does nephelometry differ from turbidimetry when measuring immune complexes?
Nephelometry detects light scattered by particles, usually at an angle to the beam. Turbidimetry measures the reduction in light passing straight through, similar to absorbance.
In the polymerase chain reaction, during which step do the primers bind to complementary sequences on the single-stranded template?
Annealing is performed at a lower temperature so primers hybridize to their targets. Denaturation separates strands; extension is when the polymerase synthesizes new DNA.
How many grams of sodium chloride are needed to prepare 500 mL of a 0.9% (w/v) saline solution?
0.9% w/v means 0.9 g per 100 mL. For 500 mL: 0.9 × 5 = 4.5 g. 9.0 g would be needed for 1 L, not 500 mL.
A 100 mg/dL standard gives an absorbance of 0.25. A patient sample treated the same way gives 0.40. Assuming Beer's law is obeyed, the patient concentration is:
Cu = (Au/As) × Cs = (0.40/0.25) × 100 = 160 mg/dL. 62.5 mg/dL results from inverting the ratio.
Immediately after a needlestick injury with a used needle, the worker should first:
CDC advises washing the wound with soap and water, then reporting at once so post-exposure evaluation and prophylaxis can start promptly. Squeezing or applying caustic agents is not recommended.
Which specimen is acceptable for anaerobic culture?
Anaerobic culture needs specimens collected without contact with normal flora, such as aspirates or tissue sent in anaerobic transport. Sputum, voided urine and surface swabs are contaminated with anaerobic flora.
Which components of MacConkey agar inhibit gram-positive bacteria?
Crystal violet and bile salts make MacConkey selective for gram-negative bacteria. Lactose with neutral red is the differential system showing lactose fermentation as pink colonies.
A traveller has sustained fever and relative bradycardia in the first week of illness. Which specimen gives the best chance of isolating Salmonella Typhi?
Blood culture is most sensitive in the first week of enteric fever. Stool and urine cultures become positive more often from the second or third week.
Watery travellers' diarrhoea caused by heat-labile and heat-stable enterotoxins is typical of which E. coli pathotype?
ETEC produces LT and/or ST toxins causing secretory diarrhoea and is the leading cause of travellers' diarrhoea. EHEC produces Shiga toxin and bloody diarrhoea.
On mannitol salt agar, a yellow halo around colonies means the organism:
Mannitol fermentation produces acid, turning phenol red indicator yellow; this is typical of S. aureus. The 7.5% salt is the selective agent.
Runyon group IV mycobacteria, such as M. fortuitum and M. abscessus, are defined by:
Rapid growers form mature colonies in less than 7 days on subculture, unlike slow growers that need several weeks. Pigment after light exposure defines group I.
A mold from an ear swab has a white surface that turns black ('salt and pepper'), with a pale reverse. Microscopy shows large round vesicles fully covered by biseriate phialides. The organism is:
Black conidial heads with a pale reverse and a radiate head covered by biseriate phialides are typical of A. niger, a common cause of otomycosis. Dematiaceous molds such as Alternaria have a dark reverse.
Branching conidiophores with metulae and phialides bearing chains of conidia, forming a 'brush-like' structure, describe:
The penicillus (brush) of Penicillium consists of branched metulae and phialides without a vesicle. Aspergillus conidiophores end in a swollen vesicle.
Routine fungal cultures for suspected dimorphic pathogens should be held before reporting 'no growth' for at least:
Dimorphic fungi such as Histoplasma and Blastomyces may take several weeks to grow, so cultures are held for about 4 weeks. Shorter holding times risk false-negative reports.
Which handling best preserves Neisseria gonorrhoeae in a genital swab for culture?
Gonococci are very sensitive to cold and drying. Direct inoculation onto pre-warmed selective medium with 3–7% CO2 gives the best recovery; refrigeration kills the organism.