1. Application of Westgard multi rules in medical laboratories
Dr. Meliyanthi Gunatillaka
Consultant Chemical Pathologist
National Hospital of Srilanka
Colombo

2. Internal Quality Control (IQC)
Components of Quality Assurance
Internal Quality Control (IQC)
Steps taken by all health care professionals in their day to day activities to ensure generation of reliable laboratory results. (Prospective activity)
Pre-analytical phase
Analytical phase
Post-analytical phase
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3. Components of Quality Assurance cont…
External Quality Assessment (EQA)
Organized Inter-laboratory comparison
Tool to assess IQC to improve performance Performed by an independent agency Retrospective and periodic
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4. Validated analytical methods
Control of analytical phase
Validated analytical methods
Calibration of analytical procedure using traceability established calibration material
Quality control material in the assay
Monitor the performance by Levy Jennings charts
Application of Westgard multi rules
Equipment & Reagents
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5. Measurement Procedure Is used to determine the value of a quantity
This estimate contains a measurement error, which is the difference between the obtained value and the true value of the measurand.
Measurement error has 2 components: Random error & systematic error
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6. Measurement Accuracy Is the extent of the agreement between the result of a measurement and the true value. ( True value of an analyte is obtained by using a reference method and CRM with stated uncertainties and traceability.)( Practically not possible) (Approximations are obtained using QC material) Accuracy encompasses the concepts of precision and trueness ( Earlier it was only the trueness)
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7. ACCURACY
PRECISION Is the extent of agreement between independent results of repeated measurements
Imprecision :Expressed as SD or Coefficient ofVariation CV mmol/L or CV %
TRUNESS Is the extent of agreement between the mean value of repetitions and the true value of the measured
Expressed as a % of difference between the mean value of multiple repetitions and the true value.
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8. Random error
Is an unpredictable analytical variation which influence each measurement differently in either a positive or negative direction and to a different extent in magnitude.
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9. Possible causes of imprecision are Wrong pipetting technique
Variable reaction timing and temperature
of measurement procedures
Instrument instability
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10. Systematic error (bias)
Constant systematic bias denotes a constant difference between the true value and the observed value regardless of the concentration level.
Proportional systematic bias denotes a difference between the true value and the observed value, which changes proportionally as the concentration level changes.
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11. Possible causes of systematic errors
Errors in the assigned value to the calibrator
Deterioration of calibration material
Incorrect sample or reagent volume pipetted
Incorrect reaction timing or temperature
Incorrect instrument setting (wavelength)
Calculation errors
Presence of interferents in samples(affect the
individual samples)
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12. Calculations
Mean
If the distribution of results is a normal Gaussian curve the mean is the total score of all the measurements divided by the number of measurements.
If not, remove the outliers (values with > 3SD) and recalculate the mean.
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13. Coefficient of variation
Standard deviation
A descriptor of the extent of dispersion of a population of test values (set of measurement data) _
SD = √(X – X )2 ÷ (N – 1 )
Coefficient of variation
Relates the SD to the actual measurement so that measurements at different levels can be compared.
CV = SD CV = SD x 100
mean mean
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14. Selection of Quality control material Control materials should be used as they were patients samples and each and every one of the steps and stages that make up measurement procedure should be followed Essential characteristics Homogenicity: No significant differences between the parts that make up a lot of the control material (dispensing errors, variability in lyophylization due to residual water and reconstitution errors) ( Check the procedure for reconstitution of QC)
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15. The component that is analysed must be stable over a
Stability
The component that is analysed must be stable over a
sufficient period of time. Once recontituted the aliquoted vials should be stored in appropriate temperatures according the manufacturers instructions. Labels : date of reconstituition
No freezing and thawing cycles.
( ALP increases if stored at C)
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16. Value of the control quantity
Value should be close to the clinical decision level or cut off levels
If various cut off values exist, a number of control material can be used with different concentrations
Physiological level : upper limit of reference range
Pathological ranges : low, medium & high
Commutability
The QC material must respond to the changes or alterations in the measurement procedure in the same way as patients samples.
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17. Matrix varies from lot to lot
Types of QC material
Defined matrix material : non biological or systhetic matrix in the form of buffers, stabilizing agents
Biological matrix: Derived from biological fluids, blood,plasma,serum & urine
Matrix varies from lot to lot
Human origin : especially for immunoassays
Animal origin: cheaper and less risk of infections
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18. If not : peer review world wide values : local agent iif
Quality Control materials with assigned values
Manufacturers assigned value
Method & instrument specific value
Details of the certified reference material used
( with UM & stated references)
Range and standard deviation should be given
Laboratory assigned value
The mean value obtained following minimum of 20 repititions should fall within the 2SD of the method & instrument specific assigned value of the manufacturer ( preferably within the UM)
If not : peer review world wide values : local agent
iif
26 April 2017

19. How do we find the mean glucose value of the in-house QC sample?
Perform the glucose test under optimum conditions for minimum 20 times
Example 01- Obtained Readings
1-120, 2-120, 3-120, 4-120, 5-119, 6-120, 7-120, , 9-120, ,
11-120, , , , , , , , , ,
Mean =
Standard Deviation = 0.45
+1 s = =
- 1s = o =
+2s = x 0.45 = 120.9
- 2s = x0.45 = 119.1
+3s = x 0.45 =
-3s = x =
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20. Mean glucose under routine conditions
Perform the glucose under routine conditions for 30 days
Example 03
1-120, 2-74, 3-124, 4-120, 5-117, 6-116, 7-122, , 9-191, ,
11-120, , , , , , , , , , 21-64, , , , , , , , , ,
Corrected (After removal of outliers)
Mean SD
±1s –
±2s
±3s –
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21. Shewhart/Levey and Jennings chart
QC Charts and rules
Shewhart/Levey and Jennings chart
Analyze the QC material by the analytical method to be controlled on at least 20 times under optimal conditions and calculate the mean, standard deviation and CV % (OCV) Remove the outliers
Construct the control chart :
Y axis-control value
X axis-days
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22. QC Charts and rules cont…
Action
+3SD
Warning
+2SD
Mean
-2SD
Warning
-3SD
Action
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23. L-J Chart Analogous models…..
variance                    
Analogous models…..
L-J Chart
Symbolic Models Used in Internal Quality Control
Days
Within ±2SD – accept > 3SD –reject
between 2SD & 3SD - warning
A Trend is when six or more consecutive plots all fall in one direction, specifically upward or downward.
A shift is when six or more consecutive plots all fall on/above or below the mean line.
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24. QC Charts and rules cont…
Introduce a control specimen daily to the analytical run, plot each value on the chart.
After 20 days calculate the mean, SD and RCV, remove the outliers & recalculate the mean,SD and construct the chart, plot daily control value and follow the rules to accept/reject the run.
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25. QC Charts and rules cont… Westgard Multirule Chart and rules
Introduce two control specimens into each analytical run one for each of the two concentrations ( NORMAL & ABNORMAL)
Plot the charts with mean and SD.
12s ‘’ 1’’ Number of control observations
2s Type of error
s – Standard deviation
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26. QC Charts and rules cont…
If both control results are within 2SD from their target the batch is accepted
If at least one control result is more than 2SD from the target, the remaining rules are evaluated in turn, and the batch is rejected if any one rule is satisfied. If none is satisfied the batch is accepted.
The situation should be investigated before the next batch is analyzed
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27. Automatic chemistry analysers Normal & abnormal QC : chemistry
Daily & 50th /100th and at the end : day time
night time : at the start
Low,medium & high QC: immunoassays
Daily all 3 levels
Procedure : calibration of the method
QC:all results within 2SD : accept:run the samples
IF one QC is out, check the violations of rules in other levels. Find the cause. ( calibration) Re run the QC : IF out again : new aliquot of QC
All QC levels satisfactory – Run the samples
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28. Analogous models….. Westgard multirules
variance                    
13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
                                                                   
Analogous models…..
Westgard multirules
Symbolic Models Used in Internal Quality Control 01
13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
26 April 2017

29. Analogous models….. Westgard multirules
variance                    
13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
                                                                   
Analogous models…..
Westgard multirules
Symbolic Models Used in Internal Quality Control 02
12s refers to the control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus/minus 2s. In the original Westgard multirule QC procedure, this rule is used as a warning rule to trigger careful inspection of the control data by the following rejection rules.
26 April 2017

30. Analogous models….. Westgard multirules
variance                    
13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
                                                                   
Analogous models…..
Westgard multirules
Symbolic Models Used in Internal Quality Control 03
22s - reject when 2 consecutive control measurements exceed the same mean plus 2s or the same mean minus 2s control limit.
26 April 2017

31. Analogous models….. Westgard multirules
variance                    
13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
                                                                   
Analogous models…..
Westgard multirules
Symbolic Models Used in Internal Quality Control 04
R4s - reject when 1 control measurement in a group exceeds the mean plus 2s and another exceeds the mean minus 2s.
26 April 2017

32. Analogous models….. Westgard multirules
variance                    
13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
                                                                   
Analogous models…..
Westgard multirules
Symbolic Models Used in Internal Quality Control 05
41s - reject when 4 consecutive control measurements exceed the same mean plus 1s or the same mean minus 1s control limit.
26 April 2017

33. Analogous models….. Westgard multirules
variance                    
13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
                                                                   
Analogous models…..
Westgard multirules
Symbolic Models Used in Internal Quality Control 06
10x - reject when 10 consecutive control measurements fall on one side of the mean.
26 April 2017

34. Analogous models….. Westgard multirules
variance                    
13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
                                                                   
Analogous models…..
Westgard multirules
Symbolic Models Used in Internal Quality Control 07
8x - reject when 8 consecutive control measurements fall on one side of the mean.
26 April 2017

35. Analogous models….. Westgard multirules
variance                    
13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
                                                                   
Analogous models…..
Westgard multirules
Symbolic Models Used in Internal Quality Control
12x - reject when 12 consecutive control measurements fall on one side of the mean.
26 April 2017

36. Analogous models…. Symbolic Models Used in Internal Quality Control
variance                    
13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
                                                                   
Analogous models….
Symbolic Models Used in Internal Quality Control
What are other common multirules?
In situations where 3 different control materials are being analyzed, some other control rules fit better and are easier to apply, such as:
2of32s - reject when 2 out of 3 control measurements exceed the same mean plus 2s or mean minus 2s control limit;
26 April 2017

37. Analogous models…. Symbolic Models Used in Internal Quality Control
variance                    
13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
                                                                   
Analogous models….
Symbolic Models Used in Internal Quality Control
What are other common multirules?
31s - reject when 3 consecutive control measurements exceed the same mean plus 1s or mean minus 1s control limit.
26 April 2017

38. Analogous models…. Symbolic Models Used in Internal Quality Control
variance                    
13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
                                                                   
Analogous models….
Symbolic Models Used in Internal Quality Control
What are other common multirules?
6x - reject when 6 consecutive control measurements fall on one side of the mean.
26 April 2017

39. Analogous models…. Symbolic Models Used in Internal Quality Control
variance                    
13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
                                                                   
Analogous models….
Symbolic Models Used in Internal Quality Control
What are other common multirules?
9x - reject when 9 consecutive control measurements fall on one side of the mean.
26 April 2017

40. Analogous models…. Symbolic Models Used in Internal Quality Control
variance                    
13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
                                                                   
Analogous models….
Symbolic Models Used in Internal Quality Control
What are other common multirules?
7T - reject when seven control measurements trend in the same direction, i.e., get progressively higher or progressively lower.
26 April 2017

41. Thank you
26 April 2017