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Questions and Answers
What does a sensitivity of 90% imply about the diagnostic test?
What does a sensitivity of 90% imply about the diagnostic test?
Which of the following equations correctly represents specificity?
Which of the following equations correctly represents specificity?
If a test has a positive predictive value (PPV) of 75%, which of the following statements is true?
If a test has a positive predictive value (PPV) of 75%, which of the following statements is true?
Which of the following factors is not considered in the validation of analytical methods?
Which of the following factors is not considered in the validation of analytical methods?
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In a testing scenario where 1000 individuals were tested, if there were 875 positive tests and 275 false positives, what is the total number of true negatives?
In a testing scenario where 1000 individuals were tested, if there were 875 positive tests and 275 false positives, what is the total number of true negatives?
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What would be the negative predictive value (PNV) if there were 75 true negatives among 100 total negative results?
What would be the negative predictive value (PNV) if there were 75 true negatives among 100 total negative results?
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When identifying individuals without the disease, what does specificity measure?
When identifying individuals without the disease, what does specificity measure?
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How is the sensitivity of a test defined?
How is the sensitivity of a test defined?
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What is the acceptable range for the Coefficient Variation (CV%) in a laboratory to be considered precise?
What is the acceptable range for the Coefficient Variation (CV%) in a laboratory to be considered precise?
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Which of the following accurately describes the Z-score categories for accuracy?
Which of the following accurately describes the Z-score categories for accuracy?
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What is one of the requirements for a hematology analyzer control?
What is one of the requirements for a hematology analyzer control?
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Which of the following methods can be used to assess the accuracy of a testing method?
Which of the following methods can be used to assess the accuracy of a testing method?
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How frequently should routine quality assurance be performed?
How frequently should routine quality assurance be performed?
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When performing recovery tests, what does recovery show?
When performing recovery tests, what does recovery show?
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Which of the following is NOT part of the routine quality assurance practices?
Which of the following is NOT part of the routine quality assurance practices?
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What is the main purpose of using control sera sets in a laboratory?
What is the main purpose of using control sera sets in a laboratory?
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What is the recovery percentage calculated for a patient specimen with 50 mg/dl glucose added, if the original concentration is 100 mg/dl and the diluted test concentration is 145 mg/dl?
What is the recovery percentage calculated for a patient specimen with 50 mg/dl glucose added, if the original concentration is 100 mg/dl and the diluted test concentration is 145 mg/dl?
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Which type of standard is characterized by the highest purity and can produce a substance of exact known concentration?
Which type of standard is characterized by the highest purity and can produce a substance of exact known concentration?
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What method is used to measure systematic error from substances other than the analyte in a patient's sample?
What method is used to measure systematic error from substances other than the analyte in a patient's sample?
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Which factor does NOT typically affect normal or reference values in biological test results?
Which factor does NOT typically affect normal or reference values in biological test results?
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What can be added to a sample to minimize interference from other substances in the analytical process?
What can be added to a sample to minimize interference from other substances in the analytical process?
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What is the main characteristic of a secondary standard in comparison to a primary standard?
What is the main characteristic of a secondary standard in comparison to a primary standard?
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Which biological factor is known to specifically elevate plasma creatinine concentration after exertion?
Which biological factor is known to specifically elevate plasma creatinine concentration after exertion?
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What is the role of an internal standard in laboratory testing?
What is the role of an internal standard in laboratory testing?
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What condition is likely to cause plasma protein levels to be lower in patients?
What condition is likely to cause plasma protein levels to be lower in patients?
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How do plasma glucose levels compare to whole blood levels?
How do plasma glucose levels compare to whole blood levels?
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Which of the following factors can affect normal laboratory values?
Which of the following factors can affect normal laboratory values?
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What is required to establish whether the Beer-Lambert law can be applied in a method?
What is required to establish whether the Beer-Lambert law can be applied in a method?
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What should be compared when introducing a new analytical method?
What should be compared when introducing a new analytical method?
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Which of the following is NOT a factor to consider during the specimen collection process?
Which of the following is NOT a factor to consider during the specimen collection process?
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Why is it necessary to check the precision of an analytical method?
Why is it necessary to check the precision of an analytical method?
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What does the term 'requirements of specimen' refer to in laboratory testing?
What does the term 'requirements of specimen' refer to in laboratory testing?
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Study Notes
Method Validation
- Accuracy refers to how closely a measurement matches the true value.
- Precision is the consistency of repeated measurements.
- Sensitivity is a measure of how well a test can identify true positives - positive results in patients known to have the condition.
- Specificity is a measure of how well a test can identify true negatives - negative results in people who do not have the condition.
- Linearity refers to the range of concentrations where the measured value is directly proportional to the actual concentration.
Sensitivity and Specificity Calculations
- Sensitivity is calculated as the number of true positives divided by the total number of people with the disease, multiplied by 100%.
- Specificity is calculated as the number of true negatives divided by the total number of people without the disease, multiplied by 100%.
Positive and Negative Predictive Values
- Positive Predictive Value (PPV) indicates the probability that a positive test result is correct. It is calculated as the number of true positives divided by the total number of positive test results, multiplied by 100%.
- Negative Predictive Value (PNV) indicates the probability that a negative test result is correct. It is calculated as the number of true negatives divided by the total number of negative test results, multiplied by 100%.
Control Sera Criteria
- Availability: Sufficient quantities should be readily available.
- Stability: Stable with convenient vial volumes.
- Consistency: Minimal variation in concentration and composition between vials.
- Similarity: Close resemblance to the specimen in physical and chemical characteristics.
- Safety: Safe to use.
- Cost-effectiveness: Not expensive.
- Compatibility: Same consistency and color as human serum for hematology analyzer control.
Interpretation of Quality Control Results
- Accuracy and Precision are used to assess internal quality control results.
- Precision is considered satisfactory when the coefficient of variation (CV%) is less than 5%.
- Accuracy is determined using the z-score, which is the difference between the measured mean and the target mean, divided by the standard deviation.
Z-score Accuracy Categories
- Excellent: 0-0.5
- Satisfied: 0.5-1
- Acceptable: 1-1.5
- Poor: 1.5-2
Routine Quality Assurance
- Calibration of instruments every 3 weeks.
- Reagent Validity checks every 3 weeks.
- STD Validity checks every 3 weeks.
- Anticoagulant Validity checks every 3 weeks.
- Lab Staff Training periodically.
- Control Material Checks daily.
- Daily Control Tests with each batch of specimens.
- External Quality Control every 1 to 3 months.
- Statistical Program Check of the control system.
Measurement of Method Accuracy
- Comparison to a Reference Method: The best comparative method, but labor-intensive, complicated, and time-consuming.
- Using Control Sera Sets: As described in internal quality control.
- Recovery: Determines if a method measures all of the analyte or only part of it.
- Interference Method: Evaluates systematic error caused by substances other than the analyte, which can react with analytical reagents or alter the reaction between the analyte and the reagent.
Interference Method
- Common interferences: Hemoglobin (haemolysis), bilirubin, lipids, anticoagulants, preservatives, turbidity.
- Minimizing interference: Using blank solutions (test blank) to correct for other substances in the sample.
Standards (STD)
- STD solutions contain known concentrations of chemicals and the test substance.
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Types of STDs:
- Primary STD: Highest purity, directly measured to produce a substance of exact known concentration.
- Secondary STD: Lower purity, concentration determined by comparison to primary STD.
- Internal STD: Substance not normally present in the sample or STD, added in a known amount to correct inaccuracies.
- Arbitrary STD: Contains an unknown concentration of the analyte and is used in immunoglobulin assays.
Normal or Reference Values
- Represent the amount of a substance present in healthy individuals.
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Biological factors: Can affect normal values, including:
- Age: Example: higher alkaline phosphatase activity in growing children.
- Sex: Example: higher plasma urea levels in men.
- Diet & nutritional state: Can significantly impact test results.
- Muscular activity: Example: increased plasma creatinine after exercise.
- Posture: Example: lower plasma protein levels when lying down.
- Time of day: Example: higher T3 and T4 concentrations in the morning.
- Genetic factors: Can influence normal values.
- Other factors: Weight, menstrual cycle phase, emotional state, geographical location, climate, intrinsic haemostatic variation, race, and rural or urban living can also affect normal values.
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Laboratory factors: Impact normal values, including:
- Sample type: Example: plasma glucose is higher than in whole blood.
- Test method: Normal values vary depending on method specificity.
- Lab accuracy: Ensures precision in the measurement of normal values.
Method Description
- Analytical method: A set of instructions describing the procedure, equipment, and materials required to obtain results.
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Components of a method description:
- Principle: Explanation of the reaction or relationship between reagents and the analyte.
- Specification of reagents and instruments: Detailed information on the chemicals and equipment used.
- Calibration of STD: Establishing linearity between absorbance and concentration.
- Procedure: Step-by-step instructions for the test.
- Specimen requirements: Conditions for sample collection, such as time, anticoagulant, preservatives, and temperature.
- Reaction steps: Detailed breakdown of the reaction process.
- Calculation: Formula used to determine the final result.
- Analytical range: The range of concentrations that the method can accurately measure.
- Safety precautions: Guidelines for handling and using the materials involved.
Introducing a New Method
- Linearity check: Analyzing serial dilutions of STD to determine the linear range of absorbance and concentration.
- Precision check: Repeating runs to ensure reproducibility of results between batches and days.
- Normal subject analysis: Confirming normal values by comparing the new method to the previous one.
- Recovery check: Assessing whether the method measures all of the analyte.
- Comparison to old method: Analyzing the same patient sample using both the old and the new method.
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Description
This quiz explores the fundamental concepts of method validation in medical testing, including accuracy, precision, sensitivity, specificity, and linearity. Participants will also learn calculations for sensitivity and specificity, as well as the significance of positive and negative predictive values. Test your knowledge on how these parameters impact diagnostic accuracy.
