MLS Quality & Safety 3 — Questions and Answers
Question 1: A method validation study compares a new analyzer to a reference method using 40 patient samples. Which statistical analysis is used to assess proportional and constant bias?
- Westgard multi-rule analysis
- Passing-Bablok or Deming regression (Correct answer)
- Coefficient of variation calculation
- Gaussian distribution plot
Correct answer: Passing-Bablok or Deming regression
Passing-Bablok and Deming regression are used in method comparison studies to detect proportional and constant systematic errors between two methods.
Question 2: What is the purpose of running a blank in photometric assays?
- To calibrate the wavelength selector
- To zero the instrument and eliminate background absorbance (Correct answer)
- To verify the linearity of the detector
- To check the precision of pipetting
Correct answer: To zero the instrument and eliminate background absorbance
The reagent blank zeroes the spectrophotometer to account for background absorbance from reagents, isolating the analyte's contribution.
Question 3: A laboratory's glucose linearity study shows acceptable results from 10–500 mg/dL but not above. What should be done for patient samples with glucose above 500 mg/dL?
- Report the result with a 'greater than' symbol without dilution
- Dilute the sample and multiply the result by the dilution factor (Correct answer)
- Repeat the test twice and average the results
- Use a different reagent lot that may have higher linearity
Correct answer: Dilute the sample and multiply the result by the dilution factor
Samples exceeding the analytical measurement range must be diluted; results are then multiplied by the dilution factor to report an accurate value.
Question 4: The GHS (Globally Harmonized System) label on a chemical container includes a pictogram of a flame over a circle. This indicates the substance is:
- Flammable
- An oxidizer (Correct answer)
- Corrosive
- Toxic
Correct answer: An oxidizer
The GHS flame-over-circle pictogram specifically denotes oxidizing substances, which can intensify fires or cause spontaneous combustion.
Question 5: Which of the following is an example of a pre-analytical error affecting laboratory results?
- Reagent deterioration during the assay
- Hemolysis due to traumatic venipuncture (Correct answer)
- Incorrect calibration of the analyzer
- Software rounding errors in result reporting
Correct answer: Hemolysis due to traumatic venipuncture
Hemolysis from traumatic venipuncture is a pre-analytical error occurring before the sample reaches the analyzer, potentially falsely elevating potassium and LDH.
Question 6: A laboratory technologist notices the QC for troponin has been trending upward over 10 days without violating a Westgard rejection rule. This pattern most likely indicates:
- Random error from pipetting inconsistency
- Systematic shift due to reagent or calibration change (Correct answer)
- Gross error requiring immediate instrument shutdown
- Normal biological variation in the control material
Correct answer: Systematic shift due to reagent or calibration change
A gradual upward trend in QC data often signals systematic drift, typically caused by reagent deterioration, calibrator instability, or instrument maintenance issues.
Question 7: Under CLIA regulations, how often must laboratories perform and document calibration verification for quantitative tests?
- Monthly
- Every 6 months (Correct answer)
- Annually
- Only when reagent lots change
Correct answer: Every 6 months
CLIA requires calibration verification at least every 6 months, when reagent lots change, after major instrument maintenance, and when QC is out of range.
MLS Quality & Safety 3
A method validation study compares a new analyzer to a reference method using 40 patient samples.
Which statistical analysis is used to assess proportional and constant bias?