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WESTGARD RULES 2.pptx
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- 2. • In 1981Dr.James Westgard Of The University Of Wisconsin Published An Article On Laboratory Quality Control That Set The Basis For Evaluating Analytical Run Quality For Medical Laboratories. • The Elements Of The Westgard Systems Are Based On Principles Of Statistical Process Control Used In Industry Nation Wide Since The 1950’s • These Rules Are Used Individually Or In Combination To Evaluate The Quality Of Analytical Runs.
- 3. • The rulesof how to use LJ correctly has been described by James westgard and these are called Westgard rules. • These rules are used for detecting changes in the analytical system.
- 4. Rules for what? • To decide whether an analytical run is in-control or out –of –control • These rules can be applied as single rules and as a group of rules(multi-rules) • Westgard rules can be applied only if your qc are plotted with the range of ±3 SD
- 5. Two key factorsto keep in mind while selecting / using rules : Maximize error detection: Per cent error detection ( P ed ) >90% Minimize false rejection : Percent false rejection ( P fr ) < 5 %
- 6. 2 sets ofQC rule nomenclatures 1. N and L 2. Within / across (run / material)
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- 8. Nomenclature 2 : Within-run/ across material DATE QC LEVELS DAY I Level 1 Level 2 DAY 2 Level 1 Level 2 Across run / same material DATE QC LEVELS DAY 1 LEVEL 1 LEVEL2 DAY 2 LEVEL 1 LEVEL 2 2/3 LEVEL OF QC IN THE SAME RUN SAME LEVEL (MATERIAL) OF QC BUT IN 2 OR MORE CONSECUTIVE RUNS
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- 11. 1:2S RULE • Onecontrol exceeding the ± 2 SD limit. • Denotes a random error / beginning of a systematic error • Warning rule • It can be both in plus and in minus direction • Even In absence of any analytical errors 4.5 % of data points in the region of 1:2S region If only one level of QC is being run in the lab 1:2S has to be a rejection rule
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- 14. • one controlresult has exceeded the established mean +/- 3SD range. • Rejection rule • a run is rejected when a single control measurement exceeds the mean 3SD control limit This rule identifies unacceptable Random error Beginning of a large systematic error.
- 15. 2:2s RULE • twoconsecutive control results have exceeded the same mean +/- 2SD limit. • Rejection rule. • Identifies only systematic errors only There are two applications to this rule • With-in-run ( in the 2 levels of QC in the same run) • Across runs ( in the same QC in 2 consecutive runs )
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- 17. If a normal(level 1) and abnormal (level 2) control are >2s On the same side of mean: • This run violates the within-run application for systematic error If level 1 is accepatable and level 2 is 1:2s, the level 2 result from previous run is examined: • If level 2 in previous run was • At +2.0s or greater • Then the across run application for systematic error is violated
- 19. 2 of 32sRULE: • When 2 out of 3 control measurements exceed the same ±2SD control limit. • Denotes systematic error.
- 21. R4S RULE : •When 2 control measurements in a group exceeds the mean ±2SD on either side or if the sum of SD of two material >4 SD • Only be interpreted within-run, not across-run • Identifies random error only • Applied only within the current run.
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- 24. 31S RULE : •3 consecutive control meaurements exceed the same mean plus 1s or mean minus 1s control limit. • Denotes systematic error • 3 consecutive results • Greater than 1s • On the same side of mean • Applied for within control material or across control material
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- 26. • Within controlmaterial violations indicate systematic bias in a single area of the method curve. • While violation across control materials indicates systematic error over a broader concentration.
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- 30. 10 x RULE •The 10-x Control Rule indicates ten consecutive control results have fallen on the same side of the mean. • rejection rule
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- 32. • When 6or 8 or 9 or 10 or 12 control results on the same side of mean regardless of the specific SD in which they are located. • Within control material violations indicate systematic bias in a single area of the method curve • While violation across control materials indicates systematic error over a broader concentration.
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- 37. RULE VIOLATION SYSTEMATICERROR RANDOM ERROR 1 : 2s 2 : 2s 1 : 3s 4: 1s 2 of 3:2s 3 : 1s 10x 7T R : 4s
- 38. Within run errors (Thepower of daily monitoring) • Stop and take corrective action if a single point exceeds, 1 : 3s limit • Stop and take corrective action if two levels of control exceed, 2:2s • Stop and take corrective action, R4s limit. meant only to be applied within run.
- 39. Across run errors: ( the power of periodic review)
- 42. What do youdo now ?
- 43. Corrective actions Things thatcan go wrong • Instrument malfunction • Reagents preparations,contamination, volume • Tech error • Control specimen is old or prepared improperly Corrective action • Identify malfunction • New reagents • Identify error and repeat test • Use new control
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