Medical Laboratory Technician Exam Laboratory Operations and QC 5 — Questions and Answers
Question 1: Which of the following is the BEST indicator that a pipette is in need of recalibration?
- The pipette is more than 6 months old
- QC results show a sudden positive shift across multiple analytes (Correct answer)
- A single QC result exceeds 2 SD from the mean
- The pipette tip becomes loose during aspiration
Correct answer: QC results show a sudden positive shift across multiple analytes
A sudden positive shift in multiple analytes often points to a volumetric error such as a pipette delivering too much sample.
Question 2: Carryover in automated analyzers refers to:
- Contamination of a sample by residual material from a previous sample (Correct answer)
- Transfer of QC data to a patient result file
- Movement of reagents between different storage compartments
- Cross-reactivity of an antibody with a structurally similar analyte
Correct answer: Contamination of a sample by residual material from a previous sample
Carryover occurs when residual material from a prior sample contaminates the next sample, falsely affecting its result.
Question 3: A laboratory is comparing results from a new method to an established reference method. The best statistical tool to evaluate proportional bias is:
- Levey-Jennings chart
- Westgard multi-rule analysis
- Passing-Bablok regression (Correct answer)
- Receiver operating characteristic (ROC) curve
Correct answer: Passing-Bablok regression
Passing-Bablok regression evaluates agreement between two methods and can detect both constant and proportional bias.
Question 4: A spectrophotometer reads a standard solution that should have 0.400 absorbance but displays 0.398. This difference is an example of:
- Random error only (Correct answer)
- Systematic error only
- Both random and systematic error
- Gross error requiring instrument replacement
Correct answer: Random error only
A single small deviation from the expected value is consistent with random (imprecision) error rather than a consistent systematic bias.
Question 5: In laboratory quality management, 'total allowable error' (TEa) defines:
- The maximum difference between two QC levels
- The maximum error acceptable for a test to be clinically useful (Correct answer)
- The number of errors permitted per 1,000 patient samples
- The SD limit beyond which an instrument must be serviced
Correct answer: The maximum error acceptable for a test to be clinically useful
TEa is the maximum permissible combination of imprecision and inaccuracy for a test result to remain clinically meaningful.
Question 6: Which of the following BEST describes the purpose of an internal quality control (IQC) program?
- To compare a laboratory's results with peer laboratories nationally
- To monitor day-to-day precision and accuracy of testing processes (Correct answer)
- To certify that laboratory personnel meet competency requirements
- To verify that reagent lots meet manufacturer specifications before use
Correct answer: To monitor day-to-day precision and accuracy of testing processes
IQC monitors the ongoing performance of the testing process within the laboratory to detect errors before patient results are reported.
Question 7: A laboratory records the following QC results for sodium: 139, 138, 141, 137, 140, 142, 138 mEq/L (mean=139, SD=1.7). The R-4s rule compares:
- The highest and lowest results within a single run to the 4 SD range (Correct answer)
- Consecutive control results from the same level to the ±2 SD range
- The current run mean to the cumulative mean over 30 days
- Results from two different control levels to a single 2 SD limit
Correct answer: The highest and lowest results within a single run to the 4 SD range
The R-4s rule is violated when the range between the highest and lowest QC result within one run exceeds 4 SD, indicating random error.
Medical Laboratory Technician Exam Laboratory Operations and QC 5
Which of the following is the BEST indicator that a pipette is in need of recalibration?