Podcast
Questions and Answers
What is involved in pre-analytic quality assurance?
What is involved in pre-analytic quality assurance?
Why should precision and accuracy be tested when getting a new method of testing or instrument?
Why should precision and accuracy be tested when getting a new method of testing or instrument?
What are the criteria for selecting a new method or instrument based on medical usefulness?
What are the criteria for selecting a new method or instrument based on medical usefulness?
What should be considered under technical issues for method selection?
What should be considered under technical issues for method selection?
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Which factor is NOT part of the technical considerations during method selection?
Which factor is NOT part of the technical considerations during method selection?
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What is the primary reason for evaluating precision and accuracy with a new analytical method?
What is the primary reason for evaluating precision and accuracy with a new analytical method?
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What are the 5 steps that must be part of method evaluation?
What are the 5 steps that must be part of method evaluation?
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What is the formula for calculating Total Error (TE)?
What is the formula for calculating Total Error (TE)?
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What is analyzed to obtain an estimate of short-term imprecision?
What is analyzed to obtain an estimate of short-term imprecision?
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What type of error occurs in one direction only and results in inaccuracy?
What type of error occurs in one direction only and results in inaccuracy?
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In long-term replication experiments, how many samples of each control material should be analyzed?
In long-term replication experiments, how many samples of each control material should be analyzed?
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What are the two types of errors that need to be tested during method validation?
What are the two types of errors that need to be tested during method validation?
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Which calculation is used to determine the coefficient of variation?
Which calculation is used to determine the coefficient of variation?
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What is the purpose of performing linearity studies?
What is the purpose of performing linearity studies?
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Which step involves checking for random errors during method evaluation?
Which step involves checking for random errors during method evaluation?
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What percentage of the defined total error should the within-run standard deviation be for short-term imprecision?
What percentage of the defined total error should the within-run standard deviation be for short-term imprecision?
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What do recovery studies measure in accuracy assessments?
What do recovery studies measure in accuracy assessments?
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What do interference studies aim to check in quality assurance?
What do interference studies aim to check in quality assurance?
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What questions can be answered through method evaluation of a new method or instrument?
What questions can be answered through method evaluation of a new method or instrument?
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What does the upper limit of linearity of a new method refer to?
What does the upper limit of linearity of a new method refer to?
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What is the significance of establishing a working Method Evaluation Plan?
What is the significance of establishing a working Method Evaluation Plan?
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Why is it important to have a procedure in place if the test sample exceeds the limit of linearity?
Why is it important to have a procedure in place if the test sample exceeds the limit of linearity?
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What determines whether a new method can be implemented after evaluation?
What determines whether a new method can be implemented after evaluation?
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What is the CLIA criterion for acceptable performance for cholesterol?
What is the CLIA criterion for acceptable performance for cholesterol?
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When comparing a new method with a reference method, what study design should be followed?
When comparing a new method with a reference method, what study design should be followed?
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How is precision typically measured in quality assurance studies?
How is precision typically measured in quality assurance studies?
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What does the accuracy of a new method compare to the reference method indicate?
What does the accuracy of a new method compare to the reference method indicate?
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What is the total error in quality assurance composed of?
What is the total error in quality assurance composed of?
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In quality assurance, how is linearity typically determined?
In quality assurance, how is linearity typically determined?
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Study Notes
Pre-analytic Quality Assurance
- Involves proper specimen collection, identification, and labeling, as well as storage and transport at the correct temperature
- Processing includes adding preservatives, and equipment and reagents must be properly received and referred or delivered for testing
Method Evaluation
- Definition: A systematic test of an analytical method to assess a procedure or instrument's performance
- Objectives: To test precision and accuracy when getting a new method or instrument
- Involves replicant studies, linearity, recovery, interference, and comparison with previous methods
Method Selection
- A new method or instrument should be chosen based on medical usefulness, financial issues, technical issues, application, methodology, and performance
- Technical issues include required personnel training, safety considerations, sample type and size, anticipated workload, and routine turnaround time
- Technical considerations include methodology characteristics, such as chemical specificity, optimum reaction conditions, and manner of calibration, as well as performance characteristics like upper limit of linearity and lower limit of sensitivity
Method Evaluation Plan
- Involves implementing a new method if the method evaluation shows acceptable results, the SOP is written, and technologists are trained
- The plan should answer questions about a new method or instrument, such as its performance, manufacturer's claims, and provision of information for patient care
- The plan includes 5 steps: instrument maintenance and calibration, technologist training, sample collection, precision check, linearity check, recovery studies, interference experiment, and comparison of methods
Method Validation
- Precision and accuracy must be tested, with precision checked first to test random errors and accuracy checked second to test systematic errors
- Part of the process to evaluate method performance
Types of Error
- Random error (precision error): due to chance and affecting precision
- Systematic error (accuracy error): due to factors like erroneous values for standards and incomplete calibration, affecting accuracy
- Total error (TE) is the sum of random error (RE) and systematic error (SE)
Systematic Error
- Error that occurs in one direction only, increasing or decreasing results by the same amount
- Due to factors like erroneous values for standards, incomplete calibration, and shifts in reagent baseline
- Results in inaccuracy
Linearity
- Example: cholesterol levels with a linear regression equation of y = 1.001x - 0.289
- Linearity studies involve analyzing 20 samples of each material within a run or day to obtain an estimate of short-term imprecision
- Long-term replication experiment involves analyzing 1 sample of each material on 20 different days to estimate long-term imprecision
Precision Calculations
- Calculate the mean, standard deviation, and coefficient of variation for each material
- Formulae: mean = ∑xi / n, SD or s = √∑(xi-mean)² / (N-1), CV = s / mean × 100
- Determine whether short-term and long-term imprecision is acceptable based on total allowable error
Precision Acceptable Levels
- For short-term imprecision: within-run standard deviation should be ¼ or less of the defined allowable total error
- For long-term imprecision: the total standard deviation should be 1/3 or less of the defined total error
Accuracy Studies
- Types of accuracy studies: recovery studies, interference studies, and dilution (linearity) studies
- Recovery studies measure proportional systematic error and help understand bias revealed in the comparison of methods experiment
Comparison of Methods
- If reference method available, validate new method compared to reference
- Study design: analyze same samples by both methods, making sure both instruments are well maintained and calibrated
- Plot results of new method on Y-axis and reference method on X-axis, with a plot comparison line (slope 1.0 and y-intercept 0)
Accuracy of New Method
- Agreement of a measurement with the true value, indicating systematic error
- Measured with linearity, recovery, and interference studies
Summary
- Precision is measured with replicant studies, involving mean, standard deviation, and %CV
- Accuracy is measured with linearity, recovery, and interference studies
- Total error is the sum of random error (from precision study) and systematic error (from linearity or comparison of methods)
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Description
Learn about the steps involved in method evaluation for quality assurance, including precision check, linearity check, recovery studies, interference experiments, and comparison of different methods. Understand the importance of testing precision and accuracy in method validation.
