Podcast
Questions and Answers
The ______ range is defined as the range within which a certain percentage of results will fall.
The ______ range is defined as the range within which a certain percentage of results will fall.
reference
Internal and external quality ______ are important for maintaining accurate laboratory results.
Internal and external quality ______ are important for maintaining accurate laboratory results.
control
Analytical ______ and specificity are crucial for the validity of test results.
Analytical ______ and specificity are crucial for the validity of test results.
sensitivity
A ______-Bland plot is used to compare the results of two different assays.
A ______-Bland plot is used to compare the results of two different assays.
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Timely, accurate, and ______ results are essential features provided by clinical biochemistry labs.
Timely, accurate, and ______ results are essential features provided by clinical biochemistry labs.
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A ______ limit helps define the lowest concentration of an analyte that can be reliably measured.
A ______ limit helps define the lowest concentration of an analyte that can be reliably measured.
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Monitoring treatment is a key role of clinical biochemistry tests, for instance in ______ mellitus.
Monitoring treatment is a key role of clinical biochemistry tests, for instance in ______ mellitus.
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Screening for conditions like ______ is an important function of clinical biochemistry.
Screening for conditions like ______ is an important function of clinical biochemistry.
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Samples for biochemical testing can include blood, urine, and ______.
Samples for biochemical testing can include blood, urine, and ______.
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To collect a blood sample, one must use the correct ______.
To collect a blood sample, one must use the correct ______.
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It is important to ensure that the request form is ______ completed.
It is important to ensure that the request form is ______ completed.
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The anticoagulant that binds calcium ions is ______ oxalate.
The anticoagulant that binds calcium ions is ______ oxalate.
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Sodium fluoride is used to inhibit ______ and maintain glucose concentrations.
Sodium fluoride is used to inhibit ______ and maintain glucose concentrations.
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The number of adults with diabetes has ______ to 422 million.
The number of adults with diabetes has ______ to 422 million.
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Reference intervals are chosen to include ______% of the values found in healthy volunteers.
Reference intervals are chosen to include ______% of the values found in healthy volunteers.
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5% of the normal population will be ______ the reference range.
5% of the normal population will be ______ the reference range.
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The reference interval is defined as mean ± ______ SD.
The reference interval is defined as mean ± ______ SD.
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In the direct chemical reaction assay, glucose reacts with a ______ to achieve a color change.
In the direct chemical reaction assay, glucose reacts with a ______ to achieve a color change.
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______ is defined as how close the result of an assay comes to the true value.
______ is defined as how close the result of an assay comes to the true value.
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A Bland – Altman Plot is used to indicate whether there is ______ between two assays.
A Bland – Altman Plot is used to indicate whether there is ______ between two assays.
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Analytical ______ refers to how well an assay detects only a specific substance.
Analytical ______ refers to how well an assay detects only a specific substance.
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Assay 1 CV = ______%
Assay 1 CV = ______%
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Assay 2 CV = ______%
Assay 2 CV = ______%
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Mean + 2 SD = ______
Mean + 2 SD = ______
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SD for Assay 1 is ______ e-4
SD for Assay 1 is ______ e-4
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SD for Assay 2 is ______ e-4
SD for Assay 2 is ______ e-4
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Detection limit refers to the lowest amount of analyte which can be distinguished from ______
Detection limit refers to the lowest amount of analyte which can be distinguished from ______
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Quality Control materials are provided at various concentrations: H, M, and ______
Quality Control materials are provided at various concentrations: H, M, and ______
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The example given involves a concentration of analyte of ______ mmole/L
The example given involves a concentration of analyte of ______ mmole/L
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The Levy-Jennings chart indicates performance of a test with quality control samples over ______.
The Levy-Jennings chart indicates performance of a test with quality control samples over ______.
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In a Levy-Jennings Plot, a trend is identified when there are ______ or more points showing a consecutive move in the same direction.
In a Levy-Jennings Plot, a trend is identified when there are ______ or more points showing a consecutive move in the same direction.
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External quality control compares the performance of a lab with other labs using the same ______ and method.
External quality control compares the performance of a lab with other labs using the same ______ and method.
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Random error results in measurements that are ______ but imprecise.
Random error results in measurements that are ______ but imprecise.
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Point of Care Testing is defined as laboratory tests performed at or near a patient at or near a site where care or ______ may be provided.
Point of Care Testing is defined as laboratory tests performed at or near a patient at or near a site where care or ______ may be provided.
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Systematic error can lead to results that are precise but ______.
Systematic error can lead to results that are precise but ______.
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In quality control for instruments bought on the internet, ______ training is essential for effective result interpretation.
In quality control for instruments bought on the internet, ______ training is essential for effective result interpretation.
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Performance reports generated from external quality control assess the performance of a lab and compare it against ______ analysers measuring the same analyte.
Performance reports generated from external quality control assess the performance of a lab and compare it against ______ analysers measuring the same analyte.
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Study Notes
Biochemical Tests in Medicine
- The focus of the lecture is on ensuring the quality of results generated by biochemical tests in healthcare.
- Key principle: Results need to be timely, accurate, reproducible, and relevant.
- Clinical biochemistry lab role: Provide these results and expert interpretative advice to help with accepting or rejecting results.
Purposes of Clinical Biochemistry Tests
- Diagnosis: Helps identify diseases like myocardial infarction.
- Prognosis: Predicting the outcome of diseases.
- Screening: Identifying undiagnosed conditions like phenylketonuria (PKU) in newborn screening programs.
- Monitoring: Determining and monitoring treatment for conditions like diabetes mellitus and thyroid hormone replacement. Long-term monitoring of chronic conditions like prostate-specific antigen (PSA) levels.
Types of Samples Used for Biochemical Testing
- Blood (serum, plasma)
- Urine
- Faeces
- Cerebrospinal fluid (CSF)
- Saliva
- Sweat
- Hair
Sample Collection and Delivery to the Lab
- Proper sample selection and collection are crucial for meaningful results.
- It is important to use correct sample tubes/bottles and adhere to appropriate timing guidelines (e.g., fasting blood glucose vs. random).
- The request form must be completed correctly.
- Quick delivery to the lab is essential.
Blood Collection Tubes
- Different tubes are used for different purposes and types of blood analysis:
- SST gel: Separator gel tube for serum analysis (contains a gel that separates blood cells from serum after centrifugation).
- Potassium Oxalate: Contains an anticoagulant that binds to calcium ions.
- Sodium Fluoride: Inhibits glycolysis, preserving glucose and lactate concentrations.
Diabetes and Blood Glucose Assays
- Diagnosis of diabetes: Begins with a blood glucose assay.
- Monitoring of blood glucose: Crucial for diabetes management.
- Reference interval: 70 - 145 mg/dL
Reference Intervals/Ranges
- Reference intervals: Designed to capture 95% of results from healthy individuals, meaning 5% of the normal population will fall outside this range.
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Statistical interpretation:
- 1 Standard deviation (SD): Cover 67% of results.
- 2 SD: Cover 95% of results.
- 3 SD: Cover 99% of results.
- Reference interval/range: Typically calculated as mean ± 2 SD.
- Each lab establishes its own reference interval.
Spectrophotometric Methods of Measuring Blood Glucose Concentration
- Two common methods:
- Assay 1: Direct chemical reaction - glucose reacts with a chemical to produce a color change.
- Assay 2: Enzyme-linked reaction - glucose oxidase oxidizes glucose, releasing hydrogen peroxide. Hydrogen peroxide reacts with a substance to produce a colored product.
Assay Performance Characteristics
- Analytical Sensitivity: Smallest amount of analyte that can be detected (detection limit).
- Analytical Specificity: Ability of the assay to detect only the specific substance and not related substances.
- Accuracy: How close the result is to the true value.
- Precision: Reproducibility of repeated measurements.
- Limits of Linearity: Range of concentrations where results are accurate.
- Coefficient of Variation (CV): Measures precision; calculated as (SD/mean) x 100.
- Action Limit: Upper and lower limits that trigger further investigation of assay performance.
- Random Error: Imprecise results that vary randomly (e.g., pipetting errors).
- Systematic Error (bias): Consistent error in results (e.g., calibration issues).
Comparison of Assays: Regression Analysis, Bland-Altman Plot, and Precision Profile
- Regression Analysis: Demonstrates a relationship between data from two assays but doesn't indicate agreement.
- Bland-Altman Plot (Difference Plot): Compares the difference between results from two assays to assess agreement (within 2 SD).
- Precision Profile: Evaluates the precision (CV) of assays across different concentrations.
Detection Limit (Sensitivity)
- The lowest amount of analyte distinguishable from its absence.
- Determined by analyzing blank samples and calculating the mean + 2 SD.
Internal Quality Control
- Monitors the consistency of test results over time.
- Uses quality control materials (H, M, L) with known analyte concentrations, run regularly on the instrument.
- Data plotted on a Levy-Jennings plot to track performance and identify potential problems.
Levy-Jennings Plot
- A graph that plots quality control data over time.
- Trend: 6 or more consecutive points moving in the same direction indicates a trend or change in performance.
- Shift: 6 or more consecutive points on one side of the mean indicates a shift in performance, possibly due to bias.
Targeting of Errors
- Random Error: Accurate but imprecise (mean value is accurate, but individual results vary).
- Systematic Error (Positive Bias): Precise but inaccurate (consistent error, leading to biased results).
- Accurate and Precise: Ideal situation.
External Quality Control
- Compares laboratory results to those of other labs performing the same test.
- Uses standardized quality control samples sent to participating labs.
- UKNEQAS: UK National External Quality Assessment Service.
- Assess the overall performance of a lab and its results compared with other labs.
Point of Care Testing (POCT)
- Laboratory tests performed near the patient at the point of care.
- Examples: Blood glucose meters for diabetes management.
- QC Management: Challenges in managing quality control for POCT devices, including training, interpretation, accuracy, precision, and servicing.
Importance of Quality Control
- Internal Quality Control: Ensures the consistency of results within the lab.
- External Quality Control: Ensures the reliability of results compared to other labs.
- Together, these contribute to the accuracy and reliability of biochemical tests in medicine.
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Description
This quiz covers essential principles and purposes of biochemical tests in healthcare. It discusses the role of clinical biochemistry labs in ensuring accurate and timely results for diagnosis, prognosis, screening, and monitoring of various diseases. Test samples such as blood, urine, and cerebrospinal fluid are also highlighted.
