Medical Laboratory Technician Exam Laboratory Operations and QC 2 — Questions and Answers
Question 1: A Levey-Jennings chart shows a series of 6 consecutive QC results trending upward across the mean. What rule does this violate?
- 1-2s rule
- R-4s rule
- 10-x rule (Correct answer)
- 1-3s rule
Correct answer: 10-x rule
The 10-x rule is violated when 10 consecutive results fall on the same side of the mean or show a progressive trend.
Question 2: Which of the following best describes 'precision' in laboratory testing?
- Closeness of results to the true value
- Reproducibility of repeated measurements (Correct answer)
- Ability to detect low analyte concentrations
- Agreement between two different methods
Correct answer: Reproducibility of repeated measurements
Precision refers to the reproducibility or repeatability of results when the same sample is tested multiple times.
Question 3: When performing a delta check, the laboratory compares a patient's current result to:
- The laboratory reference range
- The previous result from the same patient (Correct answer)
- The QC mean for that analyte
- Results from a proficiency testing survey
Correct answer: The previous result from the same patient
Delta checks compare a patient's current result to their previous result to detect specimen identification errors or abrupt clinical changes.
Question 4: A reagent blank is used in spectrophotometry to:
- Set 100% transmittance with the solvent and reagents only (Correct answer)
- Calibrate the wavelength selector
- Measure the absorbance of the unknown sample
- Determine the linear range of the assay
Correct answer: Set 100% transmittance with the solvent and reagents only
A reagent blank zeroes out absorbance contributed by reagents alone so that only the analyte of interest is measured.
Question 5: Which type of error causes all results to shift consistently in one direction from the true value?
- Random error
- Systematic error (Correct answer)
- Gross error
- Proportional error
Correct answer: Systematic error
Systematic error (bias) causes a consistent, directional deviation of all results from the true value.
Question 6: The coefficient of variation (CV) is calculated as:
- (Mean / SD) × 100
- (SD / Mean) × 100 (Correct answer)
- (SD / Range) × 100
- (Mean − SD) × 100
Correct answer: (SD / Mean) × 100
CV = (SD / Mean) × 100, expressing precision as a percentage relative to the mean.
Question 7: CLIA mandates that proficiency testing samples must be tested:
- In duplicate by two different analysts
- Using the same routine workflow as patient samples (Correct answer)
- Only by the laboratory director
- Immediately upon receipt without storage
Correct answer: Using the same routine workflow as patient samples
CLIA requires PT samples to be processed using the same routine methods and personnel used for patient samples to ensure validity.
