MLS Quality Assurance & Standards 2 — Questions and Answers
Question 1: A Levey-Jennings chart shows 6 consecutive control values all falling on the same side of the mean. Which Westgard rule is violated?
- 1-2s rule
- 10x rule (Correct answer)
- R-4s rule
- 2-2s rule
Correct answer: 10x rule
The 10x rule is violated when 10 consecutive control values fall on the same side of the mean, indicating systematic error; 6 in a row triggers the warning precursor.
Question 2: Which term describes the ability of an analytical method to measure only the analyte of interest without interference from other substances?
- Precision
- Sensitivity
- Specificity (Correct answer)
- Accuracy
Correct answer: Specificity
Specificity (or selectivity) refers to the method's ability to measure only the target analyte without cross-reactivity from other compounds.
Question 3: A laboratory's troponin assay has a coefficient of variation (CV) of 15% at a low concentration. This primarily indicates a problem with:
- Accuracy
- Precision (Correct answer)
- Linearity
- Specificity
Correct answer: Precision
CV measures imprecision; a high CV at low concentrations indicates poor reproducibility (precision) of the assay at that level.
Question 4: CLIA '88 regulations require that proficiency testing samples be tested:
- In duplicate with different instruments
- By the same method used for patient samples (Correct answer)
- By a reference laboratory first
- Only during the first year of operation
Correct answer: By the same method used for patient samples
CLIA '88 mandates that PT samples be tested using the same routine methods, instruments, and personnel as patient samples to ensure valid assessment.
Question 5: Which type of error is detected by calculating the mean of control values over time?
- Random error
- Systematic error (Correct answer)
- Gross error
- Proportional error
Correct answer: Systematic error
Systematic error causes a consistent bias (shift or trend) that is detected by monitoring the mean of control values over multiple runs.
Question 6: A method comparison study yields a slope of 1.12 and a y-intercept of 0.5. What type of error does the slope indicate?
- Constant systematic error
- Proportional systematic error (Correct answer)
- Random error
- Gross error
Correct answer: Proportional systematic error
A slope significantly different from 1.0 indicates proportional systematic error, where the new method reads proportionally higher or lower than the reference.
Question 7: The delta check in laboratory quality control compares:
- Two different analytes in the same sample
- A patient's current result with their previous result (Correct answer)
- A patient's result with the population reference range
- Two QC levels run on the same instrument
Correct answer: A patient's current result with their previous result
The delta check flags results that have changed by more than an expected amount from a patient's previous value, alerting staff to possible specimen mix-up or acute change.
MLS Quality Assurance & Standards 2
A Levey-Jennings chart shows 6 consecutive control values all falling on the same side of the mean.
Which Westgard rule is violated?