Medical Laboratory Technician Exam Medical Laboratory Technician Laboratory Operations and QC 1 — Questions and Answers
Question 1: A QC chart shows seven consecutive control values all falling on the same side of the mean. Which Westgard rule does this pattern violate?
- 1-3s rule
- R-4s rule
- 10x rule (Correct answer)
- 2-2s rule
Correct answer: 10x rule
The 10x rule is triggered when ten consecutive control measurements fall on the same side of the mean, indicating a systematic shift or bias in the method. Seven consecutive points on one side is an early warning of the same trend, and the 10x rule specifically addresses this systematic error pattern.
Question 2: Which of the following best describes the chain of custody in a laboratory setting?
- A record documenting every individual who handled a specimen from collection to final disposal (Correct answer)
- A log of equipment maintenance performed during a shift
- A list of personnel authorized to release patient results
- A protocol for ordering repeat laboratory tests
Correct answer: A record documenting every individual who handled a specimen from collection to final disposal
Chain of custody is the documented record tracking every person who collected, transferred, received, or tested a specimen. It is essential in medicolegal cases to ensure specimen integrity and admissibility of results in legal proceedings.
Question 3: A technician notices that a reagent bottle has been open for three weeks, but the manufacturer's stability after opening is listed as two weeks. What is the most appropriate action?
- Continue using the reagent if QC results are still within range
- Discard the reagent and open a new bottle (Correct answer)
- Add a preservative to extend the reagent's stability
- Report the finding to the laboratory director and await instructions before discarding
Correct answer: Discard the reagent and open a new bottle
Reagents used beyond their open-vial stability period must be discarded regardless of current QC performance, because degradation may not yet be detectable but can compromise result accuracy. Following manufacturer guidelines for stability is a fundamental QC principle.
Question 4: What is the purpose of a calibration verification procedure in the clinical laboratory?
- To confirm that a new lot of reagent produces the same results as the old lot
- To confirm that the measuring system can accurately reproduce results across its reportable range (Correct answer)
- To establish the reference interval for a new patient population
- To identify sources of pre-analytical error in specimen collection
Correct answer: To confirm that the measuring system can accurately reproduce results across its reportable range
Calibration verification confirms that a calibrated instrument continues to accurately report patient values across its entire analytical measurement range (AMR). It is required at defined intervals and whenever calibration is performed, a major maintenance event occurs, or QC repeatedly fails.
Question 5: Which of the following is an example of a pre-analytical error?
- A spectrophotometer lamp nearing the end of its service life
- A blood sample collected in the wrong tube type for the ordered test (Correct answer)
- A QC result that exceeds the 2s warning limit
- A result reported to the wrong patient due to a transcription mistake
Correct answer: A blood sample collected in the wrong tube type for the ordered test
Pre-analytical errors occur before the specimen enters the testing phase and include mistakes in collection, labeling, transport, or tube selection. Using the wrong anticoagulant tube can falsely alter test results, making this a classic pre-analytical error.
Question 6: A new method is being compared to the current reference method using patient samples. Which statistical parameter best expresses the average difference in results between the two methods?
- Coefficient of variation (CV)
- Standard deviation (SD)
- Bias (Correct answer)
- Correlation coefficient (r)
Correct answer: Bias
Bias is the systematic difference between the mean result of a new method and the mean result of the reference method. While the correlation coefficient shows how linearly related the two methods are, it does not reveal whether one method reads higher or lower than the other — bias quantifies that difference directly.
Medical Laboratory Technician Exam Medical Laboratory Technician Laboratory Operations and QC 1
A QC chart shows seven consecutive control values all falling on the same side of the mean.
Which Westgard rule does this pattern violate?