CABT Laboratory Equipment 4 — Questions and Answers
Question 1: What is the primary purpose of a Coulter counter (impedance-based cell counter) in a clinical lab?
- Measuring electrolyte concentration
- Counting and sizing cells by electrical impedance as they pass through an aperture (Correct answer)
- Separating cells by density gradient
- Identifying cell surface antigens
Correct answer: Counting and sizing cells by electrical impedance as they pass through an aperture
A Coulter counter counts and measures cell size by detecting changes in electrical impedance as individual cells pass through a small aperture in an electrolyte solution.
Question 2: Which type of pipette should be used to transfer 0.05 mL of serum for a clinical chemistry assay?
- 10 mL serological pipette
- 50 µL micropipette (Correct answer)
- Transfer pipette (Pasteur)
- 25 mL volumetric pipette
Correct answer: 50 µL micropipette
A 50 µL (0.05 mL) micropipette with a calibrated disposable tip provides the accuracy required for small-volume serum transfers in clinical chemistry.
Question 3: During routine maintenance of a microscope, immersion oil is found on the 40× dry objective lens. The correct cleaning agent is:
- Ethanol (70%)
- Acetone
- Lens paper moistened with lens cleaner or xylene substitute (Correct answer)
- Distilled water
Correct answer: Lens paper moistened with lens cleaner or xylene substitute
Lens paper moistened with a lens cleaning solution or xylene substitute safely removes immersion oil without damaging optical coatings on dry objectives.
Question 4: What does 'CV%' (coefficient of variation) measure when validating laboratory equipment precision?
- The difference between measured and true values
- The percentage of random variability relative to the mean across repeated measurements (Correct answer)
- The number of measurements within acceptable range
- The percentage of samples that passed quality control
Correct answer: The percentage of random variability relative to the mean across repeated measurements
CV% = (standard deviation / mean) × 100, expressing random variability as a percentage of the mean to assess instrument precision.
Question 5: A gas chromatograph (GC) used in toxicology shows baseline noise. Which component is most likely responsible?
- Sample injector port
- Carrier gas supply
- Detector or detector contamination (Correct answer)
- Column oven fan
Correct answer: Detector or detector contamination
Detector contamination or detector malfunction is the most common cause of elevated baseline noise in gas chromatography systems.
Question 6: Which safety practice is required when transporting a compressed gas cylinder in a hospital laboratory?
- Carry it horizontally by one person
- Secure it upright in a wheeled cart with a chain or strap (Correct answer)
- Remove the regulator before transport
- Transport it only in freight elevators with no personnel
Correct answer: Secure it upright in a wheeled cart with a chain or strap
Compressed gas cylinders must be secured upright in a wheeled cart with a restraining chain or strap to prevent tipping and valve damage during transport.
Question 7: In an automated immunoassay analyzer, what is the function of the 'wash buffer' step?
- To denature the antigen before detection
- To remove unbound antibodies or conjugates, reducing background signal (Correct answer)
- To dilute the patient sample before incubation
- To calibrate the optical system
Correct answer: To remove unbound antibodies or conjugates, reducing background signal
Wash buffer steps remove unbound reactants between incubation phases, which is essential for minimizing background and achieving specific, accurate immunoassay results.
CABT Laboratory Equipment 4
What is the primary purpose of a Coulter counter (impedance-based cell counter) in a clinical lab?