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Questions and Answers
What defines an outlier in a dataset?
What defines an outlier in a dataset?
Which method is used for parametric techniques to determine reference limits?
Which method is used for parametric techniques to determine reference limits?
What is required for populations when using transferability of reference values?
What is required for populations when using transferability of reference values?
What does a reference interval imply?
What does a reference interval imply?
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What is the CLSI recommendation for verifying reference values?
What is the CLSI recommendation for verifying reference values?
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Which of the following is considered a requirement for pre-analytical considerations in transferability?
Which of the following is considered a requirement for pre-analytical considerations in transferability?
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What is the role of mathematical transferring in reference values?
What is the role of mathematical transferring in reference values?
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What is the primary focus of the interpercentile interval method?
What is the primary focus of the interpercentile interval method?
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What is the primary purpose of establishing reference intervals for clinical tests?
What is the primary purpose of establishing reference intervals for clinical tests?
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Which condition is NOT essential for a valid comparison with reference values?
Which condition is NOT essential for a valid comparison with reference values?
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Which exclusion criterion is relevant for producing health-associated reference values?
Which exclusion criterion is relevant for producing health-associated reference values?
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What sampling method is considered ideal when selecting reference individuals?
What sampling method is considered ideal when selecting reference individuals?
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What is meant by the term 'reference interval'?
What is meant by the term 'reference interval'?
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When determining reference limits, what should be inspected?
When determining reference limits, what should be inspected?
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Which statistical treatment is applied to reference values?
Which statistical treatment is applied to reference values?
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What is the significance of clinical decision limits?
What is the significance of clinical decision limits?
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What type of data should be collected for analysis methods?
What type of data should be collected for analysis methods?
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Which of the following descriptors for distribution is NOT a correct classification?
Which of the following descriptors for distribution is NOT a correct classification?
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Study Notes
Clinical Chemistry I - 0202304
- Course instructor is Mohammad QABAJAH
- Email address is [email protected]
- Course code is 0202304
Week 07 - Reference Values
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Objectives:
- Explain the need for establishing reference intervals for clinical tests.
- Detail conditions for valid comparison of lab results with reference values.
- Define exclusion criteria for creating health-related reference values.
- Detail partitioning criteria for subgrouping reference groups.
- Explain parametric and non-parametric methods for determining interpercentile intervals.
- Discuss the transferability of reference values, addressing prerequisites and solutions.
- Differentiate between reference values and reference intervals.
Decision Making: Comparison
- Medical history, physical exams, and supplemental tests lead to a diagnosis.
- If patient's attributes resemble a known disease, that disease is a potential diagnosis.
- If not, exclude that diagnosis.
In Laboratory: Decision Making by Comparison
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Reference values:
- Obtained from healthy individuals.
- Obtained from patients with diseases.
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Reference values in laboratory:
- Subject-based: from single individual
- Population-based: from a group of individuals
- Reference values must have a clearly defined description.
Comparing Observed Data
- Reference values are collected from various groups.
- Healthy people
- Undifferentiated hospital population
- People with typical diseases
Conditions to Ensure Proper Comparison
- Reference individuals' characteristics must be clearly outlined.
- The patient characteristics should be similar to the reference individuals.
- The conditions associated with the patient's lab tests must be known
- All data measurements should be the same type
- Standardized methods should be used across all results
- Clinical sensitivity, clinical specificity, and prevalence should be known
Selection of Reference Individuals
- Ideally, the entire population
- Random sampling, as large as possible (at least 120)
Exclusion Criteria
- Diseases
- Risk Factors (Obesity, Hypertension, occupation/environmental risks, genetically determined risk factors)
- Intake of pharmacologically active agents
- Specific Physiological States (Pregnancy, Stress, Excessive exercise)
Subgrouping of the Reference Group
- Factors to consider for subgrouping:
- Age
- Gender
- Physiological factors (Stage in menstrual cycle, stage in pregnancy, physical condition)
Specimen Collection
- Preanalytical standardization protocols are essential.
- Preparation of individuals before collection.
- Correct specimen collection techniques.
- Handling of the sample before analysis.
Analytical Procedures and Quality Control
- Defining components of the analytical process is crucial.
- Analysis method, including details on equipment.
- Reagents
- Calibrators
- Types of raw data
- Calculation methods
- Quality control
- Reliability criteria
Statistical Treatment of Reference Values
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Statistical Treatment of Reference Values:
- Dividing reference values into appropriate groups
- Evaluating the distribution of each group
- Determining reference limits
- Identifying outliers
Inspection of Distribution
- Display frequency distribution graphically (e.g., histogram)
- Identify patterns like unimodal, bimodal, or polymodal distributions
- Analyze the shape of the distribution
- Identify outliers (highly deviating values)
Determination of Reference Limits
- Reference interval: Upper and lower reference limits representing a specific proportion (e.g., 95%) of the population's values.
- Range: calculated as higher value minus lower value.
- Clinical decision limits help distinguish between groups (e.g. healthy, disease-specific individuals).
Identification of Outliers
- Assume a Gaussian distribution.
- Using Interquartile Range (IQR): Outliers are values that are significantly lower or higher than the expected range based on the IQR.
Quartile Formula
- Formulae for calculating the lower quartile (Q1), middle quartile (Q2) and the upper quartile (Q3).
Interquartile Range Formula
- Calculate the Interquartile range (IQR) by subtracting the lower quartile (Q1) from the upper quartile (Q3).
Outliers Formula
- Calculates limits for outliers based on values calculated using the quartile formula and the interquartile range.
Determination of Reference Limits
- Reference limit: Values that separate populations
- Clinical decision limit: Values defining critical levels for interventions, often based on statistically significant differences.
- Reference range vs. reference interval: Clear differentiation is crucial in clinical decision-making.
- Reference interval: a broader range of values encompassing a large percentage (e.g., 95%) of the reference population
Interpercentile Interval
- Simple, widely used method for estimating reference ranges, following recommendations of IFCC.
- Parametric techniques use mean and standard deviation (SD) to calculate 2.5th and 97.5th percentiles
- Formula for lower limit and upper limit of interval
- Non-parametric methods don't assume a specific distribution shape but use rank, percentiles, and confidence intervals.
Transferability/Transference of Reference Values
- Establishing comparability is required for using reference data from one lab in another
- The parameters considered are:
- Population comparability (no significant ethnic, social or environmental differences).
- The factors considered for analytical performance are:
- Proper selection and preparation
- Identical and valid analytical methods
- Valid external quality controls (EQCs)
- Necessary mathematical methods when results cannot be directly compared
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Description
This quiz covers the objectives of Week 07 in Clinical Chemistry I, focusing on the importance of establishing reference intervals for clinical tests. You'll learn about criteria for valid lab result comparisons, the distinction between reference values and intervals, and methodological approaches for determining interpercentile intervals.
