Quality Control in Clinical Laboratories

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Questions and Answers

What is the primary purpose of control material in a clinical laboratory?

  • To calibrate the measuring instruments
  • To balance the analytical equipment
  • To provide sample results to patients
  • To validate the reliability of the test system (correct)

Which of the following is NOT a characteristic of control material?

  • Should be in stable form
  • Can be used for short periods (correct)
  • Values cover medical decision points
  • Similar to test sample in matrix

What is the main distinction between a control and a calibrator?

  • Controls are used to set concentration levels, calibrators are not
  • Controls can never be similar to patient samples
  • Calibrators are always more expensive than controls
  • Controls validate tests, calibrators set measurement points (correct)

How are control limits typically determined in control charts?

<p>Based on historical data and standards (C)</p> Signup and view all the answers

Which of the following methods can be used to monitor performance in a clinical laboratory?

<p>Levey Jennings charts (B)</p> Signup and view all the answers

Which of the following phases is NOT part of the process to obtain reliable analytical methods?

<p>Marketing (A)</p> Signup and view all the answers

Which option describes the role of Westgard multirules in a laboratory?

<p>They help in interpreting laboratory control data (C)</p> Signup and view all the answers

What feature is essential for the selection of quality control material?

<p>It must have minimal variations in results (A)</p> Signup and view all the answers

What does '12s' in the Westgard Multi-Rule control chart indicate?

<p>One control value exceeding the mean +/- 2 standard deviations, warning (C)</p> Signup and view all the answers

What aspect does 'imprecision' in QC charts refer to?

<p>Variability in pipetting and operator inattention (A)</p> Signup and view all the answers

What is meant by 'false acceptance' in the interpretation of control charts?

<p>Accepting results that are in fact inaccurate (A)</p> Signup and view all the answers

Which rule in the Westgard Multi-Rule control chart indicates a systematic rejection?

<p>22s: Two consecutive control values exceeding the mean +/- 2s (D)</p> Signup and view all the answers

What factor could lead to 'inaccuracy' in control charts?

<p>Deterioration of instruments and reagents (B)</p> Signup and view all the answers

What does the 'R4s' rule in the Westgard Multi-Rule control chart indicate?

<p>One control value exceeding x ± 2s and another exceeding x - 2s, random rejection (C)</p> Signup and view all the answers

What is the purpose of continuous surveillance in control charts?

<p>To maintain awareness of control values over time (D)</p> Signup and view all the answers

Which of the following best describes a 'shift' in a control chart?

<p>A sudden consistent change in the control values (B)</p> Signup and view all the answers

What does imprecision in measurement refer to?

<p>Variability in the results due to random errors (D)</p> Signup and view all the answers

Which of the following is a cause of systematic errors?

<p>Deterioration of calibration material (C)</p> Signup and view all the answers

In the context of QC charts, what does a trigger between ±2SD and 3SD indicate?

<p>A warning is issued (C)</p> Signup and view all the answers

Which formula accurately describes the Coefficient of Variation (CV)?

<p>CV = SD x 100 / Mean (C)</p> Signup and view all the answers

What is the first step in implementing Quantitative Quality Control?

<p>Obtain control material (A)</p> Signup and view all the answers

What is included in a Shewhart/Levey-Jennings chart?

<p>Source of control information (A)</p> Signup and view all the answers

What does the term 'outlier' refer to in the context of QC charts?

<p>A data point outside the expected range (C)</p> Signup and view all the answers

What is the corrected mean after removing outliers for the provided glucose values?

<p>120.6 (A)</p> Signup and view all the answers

What signifies an action in the QC chart when the result exceeds +3SD?

<p>Investigate the cause (B)</p> Signup and view all the answers

How is imprecision typically expressed?

<p>As standard deviation or coefficient of variation (B)</p> Signup and view all the answers

What action should be taken if 10 consecutive control measurements fall on one side of the mean?

<p>Reject the measurements. (C)</p> Signup and view all the answers

Under what condition should two out of three control measurements be rejected?

<p>When they exceed the mean plus 2s or mean minus 2s control limits. (B)</p> Signup and view all the answers

What is indicated by seven control measurements trending in the same direction?

<p>A possible shift in system performance. (B)</p> Signup and view all the answers

What does a measurement that falls within +1SD and -1SD of the mean indicate?

<p>It is always an acceptable measurement. (C)</p> Signup and view all the answers

Which of the following describes a systematic error?

<p>Measurements consistently showing a pattern away from the mean. (B)</p> Signup and view all the answers

What types of control material are categorized for laboratory use?

<p>Frozen, freeze-dried, or chemically preserved (B)</p> Signup and view all the answers

Which source for control material can be prepared in-house?

<p>In-house pooled sera (A)</p> Signup and view all the answers

What must be adhered to when preparing and storing control materials?

<p>Manufacturer’s instructions (A)</p> Signup and view all the answers

What defines 'assayed' control material?

<p>Control material with a predetermined target value (C)</p> Signup and view all the answers

What is the main purpose of External Quality Assessment (EQA)?

<p>To assess internal quality control (A)</p> Signup and view all the answers

Which phase is NOT part of Internal Quality Control (IQC)?

<p>External validation phase (A)</p> Signup and view all the answers

Which component of measurement error is characterized by unpredictability?

<p>Random error (A)</p> Signup and view all the answers

Under the +3SD control limit, when is a run considered rejected?

<p>When a single measurement exceeds +3SD (A)</p> Signup and view all the answers

What is the criterion for rejection under the 22s rule?

<p>Two consecutive measurements exceeding mean plus 2s (C)</p> Signup and view all the answers

In the R4s rule, when should a run be rejected?

<p>When one measurement exceeds mean plus 2s and another exceeds mean minus 2s (A)</p> Signup and view all the answers

According to the 41s rule, which scenario results in a rejection?

<p>Four consecutive measurements exceeding mean plus 1s (B)</p> Signup and view all the answers

What is the primary use of the +3SD control limit in quality control?

<p>To determine if a process is in control (B)</p> Signup and view all the answers

How does the 13s rule function in quality control?

<p>It rejects when a single measurement violates either +3SD or -3SD control limits (D)</p> Signup and view all the answers

What is the threshold for rejecting results under the R4s rule?

<p>One measurement exceeding mean plus 2s and another exceeding mean minus 2s (C)</p> Signup and view all the answers

What indicates a quality control problem under the 22s rule?

<p>Two consecutive measurements exceeding the same limit (B)</p> Signup and view all the answers

Flashcards

Quality Control Material

Substances used to monitor the accuracy and precision of laboratory tests.

Calibrator

A material that contains the substance being analyzed in a known concentration. Used for calibrating instruments and setting the measuring scale.

Internal Quality Control

Regularly testing control samples to ensure the accuracy and reliability of a test method.

External Quality Assessment

External assessments involving comparison of results with other laboratories to evaluate overall performance.

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Levy-Jennings Chart

A chart designed to track the performance of a laboratory test over time, showing the control values of a specific analyte.

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Westgard Multirules

A set of rules used to assess the acceptability of laboratory control results, identifying potential errors in the testing process.

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Control of Analytical Variables

A comprehensive process encompassing the selection, evaluation, implementation, maintenance, and control of analytical methods to ensure reliable results.

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Control of Analytical Phase

Steps involved in managing analytical methods, such as calibration, quality control monitoring, and equipment maintenance.

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Assayed Control Material

Materials with a predetermined target value, used to assess the accuracy of laboratory assays.

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Unassayed Control Material

Materials with an unknown target value, requiring a full assay before use in laboratory testing.

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In-House Control Material

Control materials prepared from pooled sera within a specific laboratory, requiring a full assay and validation before use.

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Internal Quality Control (IQC)

Quality control measures performed daily by health care professionals to ensure reliable lab results, covering all stages of the testing process.

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External Quality Assessment (EQA)

A periodic comparison of results from multiple laboratories organized by an independent agency, assessing the quality of Internal Quality Control (IQC).

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Measurement Procedure

The process of determining the value of a quantity, which always includes a measurement error.

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Random Error

Unpredictable fluctuations in measurement results that can affect each measurement differently, either positively or negatively, in both magnitude and direction.

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Systematic Error

A systematic deviation in measurement results, influencing each measurement in the same direction and magnitude.

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12s Rule

A warning rule in Westgard multirule QC chart that flags one control value outside ±2 standard deviations (SD) from the mean. It suggests potential issues and requires further investigation.

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13s Rule

A rejection rule in Westgard multirule QC chart that triggers when one control value falls outside ±3 SD from the mean. It suggests a random error, prompting to repeat the run.

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22s Rule

A rejection rule in Westgard multirule QC chart that triggers when two consecutive control values are outside ±2 SD from the mean. It suggests a systematic error, needing immediate action.

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R4s Rule

A rejection rule in Westgard multirule QC chart that triggers when one control value exceeds +2 SD and the other exceeds -2 SD, indicating a random error that necessitates a repeat of the run.

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41s Rule

A rejection rule in Westgard multirule QC chart that triggers when four consecutive control values are outside ±1 SD from the mean, indicating a systematic error that requires immediate attention.

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10x Rule

A rejection rule in Westgard multirule QC chart that triggers when ten consecutive control values fall on the same side of the mean. It suggests a systematic error, requiring review and potential correction.

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Imprecision in Lab Tests

Variations in results due to factors like pipetting technique, reaction timing, and temperature.

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Control Material

A substance with a known composition, used to assess the accuracy and precision of analytical methods.

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Standard Deviation (SD)

The standard deviation (SD) of a set of measurements, representing the average variability of the data.

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Coefficient of Variation (CV)

A measure of relative variability, expressed as a percentage, calculated by dividing the standard deviation (SD) by the mean and multiplying by 100.

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Shewhart/Levey-Jennings Chart

A chart used to track the performance of analytical tests over time by plotting control values on a graph.

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Importance of QC Charts

The main aim of QC charts and rules is to monitor the performance of analytical tests, detect errors, prevent reporting of inaccurate results and maintain the reliability of laboratory testing processes.

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2 of 3 2s rule

A rule used to assess the acceptability of laboratory control results. This rule signals a problem when 2 out of 3 control measurements exceed the same mean plus 2 standard deviations (2s) or mean minus 2s control limit.

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Shift

A shift in control values means the data is consistently shifted in one direction, often indicating a systematic error.

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Standard Deviation

A measure of data dispersion, representing the average distance of individual data points from the mean.

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Quality Control

A statistical approach used in analytical laboratories to ensure the reliability and accuracy of test results.

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Study Notes

Clinical Chemistry I - 0202304

Week 09-10: Control of Analytical Variables

  • Objectives:
    • Compare internal quality control with external quality assessment programs, including needs, requirements, and features.
    • Explain the need for control materials in clinical laboratories.
    • Explain how control charts are used in clinical laboratories.
    • Describe how control limits are calculated.
    • Evaluate Levey-Jennings control charts for errors and out-of-limits data.
    • Explain Westgard multirules used to interpret laboratory control data.

Control of Analytical Phase

  • Validated analytical methods
  • Calibration of analytical procedures
  • Quality control material in the assay
  • Monitoring performance using Levey-Jennings charts
  • Application of Westgard multirules
  • Equipment and reagents

Control of Analytical Variables

  • Ensure accurate measurements using accurate methods
  • Reliable analytical methods result from a careful process involving:
    • Selection
    • Evaluation
    • Implementation
    • Maintenance
    • Control

Control Material

  • Control and Standards:
    • Control material should be appropriate for diagnostic samples.
    • Values should cover medical decision points and be similar to test sample matrix.
    • Control materials should be stable in form (aliquots or vials of suitable volume).
    • They should be usable over an extended period.

What is a Control?

  • Material containing the substance being analyzed.
  • Included with patient samples during testing.
  • Used to validate the reliability of the test system, run after instrument calibration and periodically during testing.

Control vs. Calibrator

  • Control: A substance similar to patient samples with an established concentration. Used to ensure proper procedure function.
  • Calibrator: A substance with a specific concentration. Used to set (calibrate) measuring points on a scale.

Control Material - Types and Sources

  • Types: Frozen, freeze-dried, or chemically preserved.
  • Sources: Commercially prepared, "in-house" made, or obtained from other central or reference laboratories.
  • Preparation and Storage: Adhere to manufacturer's instructions, keep adequate amounts from the same lot number, and store correctly.

Control Material - Assayed/Unassayed/"In-House"

  • Assayed: Target value predetermined; verify and use
  • Unassayed: Target value not predetermined; full assay required before use.
  • "In-House": In-house pooled sera; full assay and validation required.

Components of Quality Assurance

  • Internal Quality Control (IQC): Steps taken by health care professionals in daily activities to ensure reliable lab results (prospective activity).
    • Pre-analytical phase
    • Analytical phase
    • Post-analytical phase
  • External Quality Assessment (EQA): Organized inter-laboratory comparison, performed by an independent agency (retrospective and periodic activity). Tool to assess IQC to improve performance.

Steps in Implementing Quantitative QC

  1. Obtain control material.
  2. Run each control 20 times over 30 days.
  3. Calculate mean and +/-1,2,3 SD.

Measurement Procedure

  • Used to determine a quantity's value.
  • Estimation contains a measurement error (difference between obtained and true value).
  • Measurement error has two components: random error and systematic error.

Random Error

  • Unpredictable analytical variation influencing each measurement differently in either a positive or negative direction and to a different extent in magnitude.
  • Causes of imprecision include wrong pipetting techniques, variable reaction timing/temperatures, and instrument instability.

Systematic Errors

  • Errors in the assigned value to the calibrator.
  • Deterioration of calibration material.
  • Incorrect sample/reagent volume pipetted.
  • Incorrect reaction timing/temperature.
  • Instrument settings (wavelength) errors.
  • Calculation errors.
  • Presence of interferents in samples.

Measurement Procedure - Imprecision

  • Expressed as standard deviation (SD).
  • Expressed as coefficient of variation (CV%).

Standard Deviation/Coefficient of Variation

  • SD formulas provided
  • CV formulas provided

QC Charts and Rules - Shewhart/Levey-Jennings Chart

  • Analyze QC material using the analytical method at least 20 times under optimal conditions.
  • Calculate mean, standard deviation, and CV% (OCV).
  • Remove outliers.
  • Construct the control chart (Y-axis = control value, X-axis = days).

QC Charts and Rules - Westgard Multirule Chart

  • Introduce two control specimens into each analytical run (one normal, one abnormal) for each concentration.
  • Plot charts with mean and SD.

Westgard Multi-Rule Control Chart Rules

  • 1 2s: A single control value exceeds x ± 2s (warning).
  • 1 3s: A single control value exceeds x ± 3s (rejection).
  • 2 2s: Two consecutive control values exceed x ± 2s (rejection).
  • R4s: One observation exceeds x + 2s and another exceeds x – 2s (rejection).
  • 4 1s: Four consecutive values exceed x ± 1s (rejection).
  • 10x: Ten consecutive values fall on the same side of x (rejection).

QC Charts Rules - Continued

  • 2 of 3 2s: 2 out of 3 control measurements exceed x ± 2s (rejection).
  • 7: Seven consecutive control measurements trend in the same direction (rejection).

Examining QC Charts

  • Imprecision: Variability in pipetting, inattention to details by operator.
  • Inaccuracy: Trend (Deterioration of reagents/standards, deterioration of instrument performance), Shift (Introduction of something new to assay procedure, new lots, malfunction of instrument - immediate/permanent).

Control (Levey-Jennings) Chart interpretation

  • Continuous surveillance, visual, and statistical of control values.
  • Interpretation of results (acceptable/unacceptable).

QC Charts Summary

  • Includes test name.
  • Method of analysis.
  • Date.
  • Control source (lot #, patch #, etc.).
  • Statistical data.

Mean Glucose under Routine Conditions

  • Perform glucose tests under routine conditions for 30 days (values provided).
  • Calculate mean, standard deviation, +1 to +3 SDs, -1 to -3 SDs (values provided).
    • Re-calculate mean/SD after removing outliers (corrected values provided).

Additional Information

  • BIO-RAD Lyphochek Assayed Chemistry Control Levels 1&2 methodology (values presented in table format for different lab tests).

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