Clinical Chemistry I Week 03&04 Quiz

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Questions and Answers

Which analytical performance parameter indicates the degree to which a test produces consistent results over repeated measurements?

Dispersion

Precision (correct)

Accuracy

Calibration

What does the term 'trueness' refer to in analytical performance?

The average value of the dataset

The accuracy of a measurement relative to a true value (correct)

The variability in results

The ability to distinguish between different analytes

Which method should be used to evaluate the linearity of the response in the calibration of an analytical method?

Coefficient of variation assessment

Correlation coefficient calculation

Standard deviation analysis

Four-parameter-logistic curve analysis (correct)

In the context of method selection, what does 'Clinical Sensitivity' refer to?

The method's effectiveness in identifying true positives Signup and view all the answers

What statistical term is used to describe the average deviation of individual measurement values from the mean?

Standard deviation Signup and view all the answers

Which of the following is NOT a part of the practical criteria for method selection?

Analytical range Signup and view all the answers

What impacts the stability of calibration in modern automated machines?

Variations in response which are minimal Signup and view all the answers

What does the term 'Limit of Detection' refer to in analytical methods?

The smallest concentration that can be reliably detected Signup and view all the answers

What is one inherent risk of non-monotonic calibrator functions in analytical method calibration?

Inaccurate measurement results Signup and view all the answers

Which of the following parameters aid in understanding the overall throughput of an automated method?

Time to report Signup and view all the answers

What is the primary distinction between trueness and accuracy in measurement?

Trueness involves the average of measurements being close to the true value, while accuracy pertains to individual measurements. Signup and view all the answers

Which term describes the error caused by the instability of instruments or reagents over time?

Drift Signup and view all the answers

In the context of analytical measurement, what does limit of detection (LoD) primarily indicate?

The smallest amount of analyte that can be reliably quantified. Signup and view all the answers

What is emphasized when considering method selection criteria in analytical measurement?

The number and distribution of analyte concentrations in test samples. Signup and view all the answers

Which statement accurately describes the relationship between precision and imprecision?

Precision is directly measured by standard deviation (SD) or coefficient of variation (CV). Signup and view all the answers

What does the term 'reproducibility' refer to in the context of precision?

Closeness of results under varied experimental conditions. Signup and view all the answers

Which factor is NOT typically considered when evaluating analytical goals?

Use of the latest technology in analytical instruments. Signup and view all the answers

Which error type occurs when an analyte is present but not detected due to measurement failure?

Type II error Signup and view all the answers

In the Bland-Altman plot comparison method, what do the differences (X2 - X1) represent?

The systematic error between the two analytical techniques. Signup and view all the answers

What is the main principle behind the analytical sensitivity of a method?

It is influenced by the slope of the calibration curve and random variation. Signup and view all the answers

Study Notes

Clinical Chemistry I - 0202304

Course instructor: Mohammad QABAJAH
Email address: [email protected]
Course covers week 03&04, Method Selection and Evaluation

Objectives

Familiarize with three key areas for analytical method selection.
Understand analytical performance of methods.
Be aware of analytical and practical performance criteria, focusing on automated methods.
Recall statistical concepts related to analytical performance of methods.
Compare analytical performance criteria using raw data through Bland-Altman method and correlation regression.

Method Selection: Considerations

Medical Usefulness: Optimal patient care and clinical needs of the lab test.
Analytical Performance: Calibration, precision, accuracy (trueness), analytical range, detection limit, clinical sensitivity and specificity are essential.
Practical Criteria: Detailed protocol, reference materials, reagent stability, technologist skill, potential hazards/waste, specimen requirements, instrument specifics, cost, computer platforms, technical support, automated procedure specifics (pipetting precision, carryover, detector imprecision, reagent stability, time-to-report, overall throughput, mean time to repair.)

Statistical Terms

Mean: Sum of values divided by the total number of values.
Standard deviation: Measures the amount of variation or dispersion of a set of values.
Coefficient of variation: The ratio of the standard deviation to the mean, expressed as a percentage.

Gaussian Probability Distribution

Measures the probability of a data point falling within a certain range around the mean.
Common values displayed include 68%, 95%, and 99.7% ranges.

Analytical Methods: Basic Terms

Calibration: Correlation between instrument signal and analyte concentration.
Linearity: Relationship between measured and expected values over the analytical range.
Trueness/Accuracy: Closeness of agreement of the average measured value with the true value.
Precision: Closeness of agreement among independent measurements.
Limit of Detection (LoD): The smallest concentration of an analyte that can be reliably detected above background noise.
Limit of Blank (LoB): The smallest concentration that can be detected without the presence of the analyte.

Calibrator

Known quantity used for calibration.
Calibration curves can be linear or curved (e.g., four-parameter logistic functions in immunoassays).
Curves should be monotonic.
Calibration signal stability and frequency are important.

Recovery: Measured concentration difference from the added amount.
Drift: Instrument or reagent instability over time.
Carryover: Influence of previously measured samples on subsequent measurements.
Bias: Difference between the average measured value and the true value.

Repeatability: Closeness of results for measurements made under identical conditions.
Reproducibility: Closeness of results from measurements made under different conditions.
Imprecision: Measured by standard deviation and coefficient of variation, and attributable to random error. Types include between-run precision and interlaboratory precision.

Analytical Measurement Range and Limits of Quantification

Reportable range over which measurements are within the established imprecision and bias tolerances for that method.

Analytical Range

The range of concentrations where measurements are reliable and within tolerated levels of imprecision and bias.

Limit of Detection (LoD) & Limit of Blank (LoB)

Important for analytes such as hormones; factors like instrument sensitivity, sample matrix, background noise, and analyte properties impact these limits.

Analytical Sensitivity

Indicates the ability of the method to detect small changes in analyte concentration.
Slope of the calibration curve is directly related
Random variability (precision) (inverse relationship)

Analytical Specificity and Interference

The ability of a procedure to accurately measure a specific analyte, even if other substances are present.

Analytical Goals

Based on clinical outcomes or setting, biological variability, imprecision (bias <0.25× (σ2within-B + σ2 between-B)0.5 ), standards from regulatory bodies.

Method Comparison

Comparison study considerations include sample number, analyte concentration distribution, sample representativeness, practical aspects (storage, sample treatment, anticoagulants, time for measurements), and ethical issues.
Bland-Altman plot and regression analysis are used to evaluate the differences between methods.

Comparison of Methods—Proportional random error

Depends on the change in a variable, directly related.

Comparison of Methods—Traceability

Unbroken chain of comparisons to known reference standards. Includes calibration chain connecting to primary national/international standards.

Comparison of Methods—Uncertainty

Parameter characterizing the dispersion of measurement values.
Values expressed with standard deviation and probability (e.g., 95%).
Affected by preanalytical variation, method imprecision, sample-related interferences, uncertainties related to calibration, and bias corrections.

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Description

This quiz tests your understanding of analytical method selection and evaluation in clinical chemistry. Focus areas include medical usefulness, analytical performance, and practical criteria essential for optimizing lab tests. Have a firm grasp of statistical methods and performance evaluation techniques for assessment.