Medical Laboratory TechnicianĀ Exam Laboratory Operations and QC 4 ā Questions and Answers
Question 1: The Westgard 2-2s rule is triggered when:
- One control result exceeds the mean by 3 SD
- Two consecutive controls exceed the mean by 2 SD in the same direction (Correct answer)
- Two controls differ from each other by more than 4 SD
- Ten consecutive results fall on one side of the mean
Correct answer: Two consecutive controls exceed the mean by 2 SD in the same direction
The 2-2s warning rule is triggered when two consecutive QC results exceed Ā±2 SD on the same side, suggesting systematic error.
Question 2: Which of the following actions is MOST appropriate when a QC result violates a rejection rule before reporting patient results?
- Report patient results and repeat QC later
- Hold patient results, identify the problem, and repeat QC (Correct answer)
- Adjust the QC mean to accept the result
- Report only results that fall within the reference interval
Correct answer: Hold patient results, identify the problem, and repeat QC
Patient results must be held until the QC problem is identified and corrective action is verified by repeat QC.
Question 3: A laboratory notices that serum potassium results are falsely elevated on specimens left at room temperature for several hours. This is due to:
- Bacterial contamination of the specimen
- Evaporation concentrating the analyte
- Leakage of potassium from red blood cells (Correct answer)
- Oxidation of potassium by atmospheric oxygen
Correct answer: Leakage of potassium from red blood cells
Red blood cells contain high intracellular potassium; prolonged contact with serum at room temperature causes leakage, elevating results.
Question 4: The term 'analytical sensitivity' in laboratory testing refers to:
- The proportion of disease-positive patients with a positive test result
- The lowest detectable concentration of an analyte (Correct answer)
- The ability of the test to avoid false-positive results
- The agreement between two testing methods
Correct answer: The lowest detectable concentration of an analyte
Analytical sensitivity is the lowest analyte concentration reliably detected by the assay, also called the limit of detection.
Question 5: A laboratory wants to verify the manufacturer's claimed reference interval for a new analyzer. The minimum number of reference samples recommended by CLSI is:
- 10
- 20 (Correct answer)
- 40
- 120
Correct answer: 20
CLSI EP28-A3c recommends a minimum of 20 reference individuals to verify a manufacturer's claimed reference interval.
Question 6: Which of the following is a characteristic of random error?
- It shifts all results in the same direction
- It can be corrected by recalibrating the instrument
- It is unpredictable and affects precision (Correct answer)
- It is identified by trending on a Levey-Jennings chart
Correct answer: It is unpredictable and affects precision
Random errors are unpredictable and cause scatter around the mean, degrading precision without a consistent directional bias.
Question 7: Which laboratory document defines the specific steps for performing a test, including specimen requirements, reagents, and result interpretation?
- Quality assurance plan
- Standard operating procedure (SOP) (Correct answer)
- Proficiency testing report
- Laboratory compliance manual
Correct answer: Standard operating procedure (SOP)
A standard operating procedure (SOP) provides detailed, step-by-step instructions for performing a specific laboratory test.
Medical Laboratory TechnicianĀ Exam Laboratory Operations and QC 4
The Westgard 2-2s rule is triggered when: