STP Laboratory Practice 4 — Questions and Answers
Question 1: What is the appropriate response when a laboratory worker discovers an unlabeled container of unknown liquid?
- Smell the liquid carefully to help identify it
- Dispose of it immediately in the nearest drain
- Treat it as hazardous, label it 'Unknown,' isolate it, and report it to the safety officer (Correct answer)
- Test a small amount on the skin to check for reactivity
Correct answer: Treat it as hazardous, label it 'Unknown,' isolate it, and report it to the safety officer
Unknown chemicals must be treated as hazardous, properly quarantined, and reported so they can be characterized safely before any further handling or disposal.
Question 2: In the context of laboratory quality systems, what does 'traceability' mean for a measurement result?
- The ability to locate a sample within the laboratory storage system
- The property of a measurement result that can be related to a stated reference through an unbroken chain of calibrations (Correct answer)
- Tracking which analyst performed each test
- The log of all instruments used in a procedure
Correct answer: The property of a measurement result that can be related to a stated reference through an unbroken chain of calibrations
Metrological traceability links a measurement result to a national or international standard through an unbroken documented calibration chain.
Question 3: Which of the following best describes the purpose of a blank sample in an analytical run?
- To serve as the highest concentration calibration point
- To detect background signal, contamination, or matrix interference in the absence of the analyte (Correct answer)
- To verify that the instrument is properly calibrated
- To provide a sample with a known concentration for accuracy assessment
Correct answer: To detect background signal, contamination, or matrix interference in the absence of the analyte
A blank contains all components of the assay except the analyte, so any signal detected indicates background noise or contamination.
Question 4: When working with a biological safety cabinet (BSC), which action will DISRUPT the protective airflow and should be avoided?
- Keeping the sash at the designated working height
- Rapidly moving arms in and out of the cabinet (Correct answer)
- Placing materials inside before beginning work
- Using a UV light to decontaminate the cabinet before use
Correct answer: Rapidly moving arms in and out of the cabinet
Rapid arm movements across the cabinet opening create turbulence that disrupts the air curtain, allowing potential cross-contamination or exposure.
Question 5: A pipette is calibrated to deliver 1000 µL. During a gravimetric check using water at 20°C, it consistently delivers an average of 985 µL. This is an example of:
- Random error with good precision
- Systematic error (bias) with acceptable precision (Correct answer)
- Poor precision and poor accuracy
- Acceptable performance within normal variation
Correct answer: Systematic error (bias) with acceptable precision
A consistent offset in the same direction from the true value represents systematic error (bias), which can often be corrected through recalibration.
Question 6: Under OSHA's Bloodborne Pathogen Standard, what is the engineering control required to minimize needlestick injuries?
- Requiring double-glove use for all phlebotomy procedures
- Using safety-engineered sharps devices with built-in protection mechanisms (Correct answer)
- Disposing of all sharps in biohazard bags rather than rigid containers
- Recapping needles using a two-handed technique after use
Correct answer: Using safety-engineered sharps devices with built-in protection mechanisms
OSHA mandates the use of sharps with engineered sharps injury protections (SESIPs) as the primary engineering control to prevent needlestick injuries.
Question 7: What is the purpose of running a quality control (QC) sample at the beginning of each analytical batch?
- To warm up the instrument before processing patient samples
- To verify that the analytical system is performing within acceptable limits before results are reported (Correct answer)
- To calibrate the instrument to a new standard curve
- To clean the instrument's detector between runs
Correct answer: To verify that the analytical system is performing within acceptable limits before results are reported
QC samples with known values confirm that the assay and instrument are performing correctly before patient or experimental results are accepted.
STP Laboratory Practice 4
What is the appropriate response when a laboratory worker discovers an unlabeled container of unknown liquid?