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.
Timely, accurate, and ______ results are essential features provided by clinical biochemistry labs.
Timely, accurate, and ______ results are essential features provided by clinical biochemistry labs.
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.
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.
Screening for conditions like ______ is an important function of clinical biochemistry.
Screening for conditions like ______ is an important function of clinical biochemistry.
Samples for biochemical testing can include blood, urine, and ______.
Samples for biochemical testing can include blood, urine, and ______.
To collect a blood sample, one must use the correct ______.
To collect a blood sample, one must use the correct ______.
It is important to ensure that the request form is ______ completed.
It is important to ensure that the request form is ______ completed.
The anticoagulant that binds calcium ions is ______ oxalate.
The anticoagulant that binds calcium ions is ______ oxalate.
Sodium fluoride is used to inhibit ______ and maintain glucose concentrations.
Sodium fluoride is used to inhibit ______ and maintain glucose concentrations.
The number of adults with diabetes has ______ to 422 million.
The number of adults with diabetes has ______ to 422 million.
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.
5% of the normal population will be ______ the reference range.
5% of the normal population will be ______ the reference range.
The reference interval is defined as mean ± ______ SD.
The reference interval is defined as mean ± ______ SD.
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.
______ 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.
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.
Analytical ______ refers to how well an assay detects only a specific substance.
Analytical ______ refers to how well an assay detects only a specific substance.
Assay 1 CV = ______%
Assay 1 CV = ______%
Assay 2 CV = ______%
Assay 2 CV = ______%
Mean + 2 SD = ______
Mean + 2 SD = ______
SD for Assay 1 is ______ e-4
SD for Assay 1 is ______ e-4
SD for Assay 2 is ______ e-4
SD for Assay 2 is ______ e-4
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 ______
Quality Control materials are provided at various concentrations: H, M, and ______
Quality Control materials are provided at various concentrations: H, M, and ______
The example given involves a concentration of analyte of ______ mmole/L
The example given involves a concentration of analyte of ______ mmole/L
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 ______.
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.
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.
Random error results in measurements that are ______ but imprecise.
Random error results in measurements that are ______ but imprecise.
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.
Systematic error can lead to results that are precise but ______.
Systematic error can lead to results that are precise but ______.
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.
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.
- 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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