Podcast
Questions and Answers
What is the first step in calculating the mean value from ELISA test results?
What is the first step in calculating the mean value from ELISA test results?
In a normal distribution, how are values arranged around the mean?
In a normal distribution, how are values arranged around the mean?
Which metric is NOT relevant to the quality control of assaying?
Which metric is NOT relevant to the quality control of assaying?
What is indicated by a value of 270 mg/dL in the provided data set?
What is indicated by a value of 270 mg/dL in the provided data set?
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What is the purpose of dividing each OD by its corresponding CO in calculating the mean?
What is the purpose of dividing each OD by its corresponding CO in calculating the mean?
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What is the primary purpose of a QC program in a laboratory?
What is the primary purpose of a QC program in a laboratory?
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Which element is essential for a QC program according to the provided guidelines?
Which element is essential for a QC program according to the provided guidelines?
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When should the results of patient testing be released?
When should the results of patient testing be released?
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Which of the following actions is part of the QC program requirements?
Which of the following actions is part of the QC program requirements?
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What role does statistical analysis play in a QC program?
What role does statistical analysis play in a QC program?
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What is the primary purpose of quality control for quantitative tests?
What is the primary purpose of quality control for quantitative tests?
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Which of the following is NOT a step in the implementation of quality control?
Which of the following is NOT a step in the implementation of quality control?
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In the context of quality control, what does a control material signify?
In the context of quality control, what does a control material signify?
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Which chart is commonly developed to monitor control values in quality control?
Which chart is commonly developed to monitor control values in quality control?
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What separates accuracy from precision in quality control terminology?
What separates accuracy from precision in quality control terminology?
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What is a key action when addressing 'out of control' problems in quality control?
What is a key action when addressing 'out of control' problems in quality control?
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The responsibility assigned during the implementation of quality control primarily includes which of the following?
The responsibility assigned during the implementation of quality control primarily includes which of the following?
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Which of the following describes the role of control materials in testing?
Which of the following describes the role of control materials in testing?
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Which statement accurately reflects the relationship between accuracy and precision?
Which statement accurately reflects the relationship between accuracy and precision?
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What is the probability of a random measurement falling within two standard deviations of the mean in a normal distribution?
What is the probability of a random measurement falling within two standard deviations of the mean in a normal distribution?
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What does the coefficient of variation (CV) represent?
What does the coefficient of variation (CV) represent?
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Which term refers to the difference between the expectation of a test result and an accepted reference value?
Which term refers to the difference between the expectation of a test result and an accepted reference value?
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How is standard deviation (SD) calculated in a laboratory setting?
How is standard deviation (SD) calculated in a laboratory setting?
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What should be done if the control results are outside ± 2SDs?
What should be done if the control results are outside ± 2SDs?
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Which type of error requires correction of the source before results can be used?
Which type of error requires correction of the source before results can be used?
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What does measurement uncertainty represent in a quantitative test?
What does measurement uncertainty represent in a quantitative test?
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What is the primary function of control materials in quantitative QC?
What is the primary function of control materials in quantitative QC?
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Which of the following is a sign of a systematic error?
Which of the following is a sign of a systematic error?
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According to the Westgard multirule system, what is considered a better practice in quality control?
According to the Westgard multirule system, what is considered a better practice in quality control?
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Which of the following characteristics is NOT essential for control materials?
Which of the following characteristics is NOT essential for control materials?
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What action should be taken if a quality control issue is detected?
What action should be taken if a quality control issue is detected?
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What type of control material requires a full assay before it can be used?
What type of control material requires a full assay before it can be used?
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When running controls for quantitative QC, how many times should each control be tested over 30 days?
When running controls for quantitative QC, how many times should each control be tested over 30 days?
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Which factor is not typically associated with quality control issues?
Which factor is not typically associated with quality control issues?
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Which of the following is a measure of central tendency?
Which of the following is a measure of central tendency?
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What range of standard deviations is typically accepted for measurement uncertainty?
What range of standard deviations is typically accepted for measurement uncertainty?
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What does the symbol ∑ represent in calculations?
What does the symbol ∑ represent in calculations?
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Which storage method is NOT suitable for control materials?
Which storage method is NOT suitable for control materials?
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What is the goal when assessing variability in control testing?
What is the goal when assessing variability in control testing?
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What is a critical aspect of preparing control materials for quantitative QC?
What is a critical aspect of preparing control materials for quantitative QC?
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What does 'in-house' control material require before use?
What does 'in-house' control material require before use?
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Study Notes
Process Control: Quality Control for Quantitative Tests
- Quantitative tests measure the quantity of a substance in a sample
- Quality control for quantitative tests ensures accurate and reliable patient results
- A quality management system includes organization, personnel, equipment, purchasing and inventory, process control, information management, documents and records, occurrence management, assessment, process improvement, customer service, and facilities and safety
- Learning objectives include differentiating accuracy and precision, selecting control material, establishing acceptable control limits, explaining Levey-Jennings charts, and describing how to correct "out of control" problems.
What is a Control?
- Control material contains the substance being analyzed
- It's included with patient samples during testing
- Controls validate the test system's reliability
- Controls are run after instrument calibration and periodically during testing
Calibrators vs. Controls
- Calibrators are substances with a specific concentration
- Calibrators set the measuring points on a scale
- Controls are substances similar to patient samples with established concentrations
- Controls ensure the procedure works properly
Characteristics of Control Materials
- Control materials are appropriate for the diagnostic sample
- Control values cover medical decision points
- Control materials are similar to test samples (matrix)
- Controls are available in large quantities, ideally enough for one year
- Controls can be stored in small aliquots
Types of Control Materials
- Control materials may be frozen, freeze-dried, or chemically preserved
- Reconstitution may be required for certain types
Sources of Control Materials
- Control materials can be commercially prepared
- Control materials can be made in-house
- Control materials can be obtained from other laboratories (usually central or reference)
Control Materials: Assayed vs. Unassayed
- Assayed controls have predetermined target values and are verified before use
- Unassayed controls do not have predetermined target values and require full assay before use
- In-house pooled sera are unassayed controls
Choosing Control Materials
- Control values cover medical decision points
- Control materials are similar to patient samples
- Controls are typically available in high, normal, and low ranges
Preparation and Storage of Control Material
- Adhere to manufacturer's instructions
- Maintain an adequate amount of the same lot number
- Store controls correctly
Steps in Implementing Quantitative QC
- Obtain control materials
- Run each control 20 times over 30 days
- Calculate the mean and ±1, 2, and 3 standard deviations
Measurement of Variability
- Variability in control tests is normal
- Variability can be affected by the operator, environmental conditions, and performance characteristics of the measurement
- The goal is to differentiate between variability from chance and that due to error
Measures of Central Tendency
- Data sets cluster around a central value (or mean)
- The three are Mode, Median, Mean
Symbols Used in Calculations
- ∑ represents the sum of all data points
- n represents the number of data points
- Xi represents each individual measurement
Calculation of Mean
- The mean is calculated by summing all measurements and dividing by the total number of measurements
Calculation of Mean: ELISA Tests
- Run controls 20 times in 30 days
- Record OD (optical density) and cut-off values
- Divide OD by CO
- Sum the ratios and divide by the number of measurements
Data Showing Outlier
- Data showing an outlier are provided (numeric values)
Normal Distribution
- All values are distributed symmetrically around the mean
- A characteristic "bell-shaped" curve
- Assumed for all quality control statistics
Quality Control
- Quality control is used to monitor the accuracy and precision of the assay
- Accuracy is the closeness of measurements to the true value
- Precision is the amount of variation in measurements
- Bias is the difference between the expectation of a test result and an accepted reference value
Accuracy and Precision
- A graphic representation of accurate and precise, precise but biased, and imprecise results is provided
Standard Deviation and Probability
- For a normally distributed set of data, a random measurement will fall within:
- ±1 SD 68.3% of the time
- ±2 SD 95.5% of the time
- ±3 SD 99.7% of the time
Standard Deviation (SD)
- SD is the principle measure of variability
- Formula for calculating SD provided
Coefficient of Variation (CV)
- CV is the SD expressed as a percentage of the mean
Levey-Jennings Chart
- A graphical representation of control ranges
Statistics for Quantitative QC
- Assay control materials at least 20 points over 20–30 days
- Ensure procedural variations are represented
- Calculate the mean and ±1, 2, and 3 standard deviations
Draw lines for Mean and SDs
- Provide an example of a chart with lines for mean and SDs (and a calculation)
Levey-Jennings Chart
- Plot daily control measurements
Number of Controls
- Interpretation of QC depends on the number of controls run
- Good: One control - accept results within ±2SD unless shift or trend
- Better: Two levels of controls - apply Westgard multirule system
Detecting Error
- Random error: variation in QC results with no pattern—only a cause for rejection if outside 2SDs.
- Systematic error: not acceptable; correct the source of error
- Examples of systematic error:
- Shift—control on one side of the mean 6 consecutive days
- Trend—control moving in one direction, heading toward “out of control” value
Solving Out-of-Control Problems
- Identify the problem
- Refer to established policies and procedures
Possible Problems
- Degradation of reagents/kits
- Control material degradation
- Operator error
- Failure to follow instructions
- Outdated procedure manuals
- Equipment failure
- Calibration error
Summary
- A quality control program is essential for quantitative tests
- A program should monitor all quantitative tests, have written policies and procedures followed by lab staff, and provide for troubleshooting and corrective action
- A quality control manager should monitor and review QC data; use statistical analysis; provide for good records
Key Messages
- A quality control program differentiates normal variation from error
- QC programs monitor accuracy and precision
- Do not release patient results if QC doesn’t meet target values
Questions?
- A section indicating space for questions or comments
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Description
This quiz tests your knowledge on the statistical concepts and calculations relevant to analyzing ELISA test results. You will explore the steps in calculating the mean, understand the distribution of values, and evaluate quality control metrics. Test your understanding of how to interpret specific values in the context of ELISA data.
