WESTGARD RULES

1. WESTGARD RULES

2. • In 1981 Dr.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 rules of 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 factors to 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 of QC rule nomenclatures
1. N and L
2. Within / across (run / material)

7. Nomenclature 1:

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

9. Gaussian curve

10. 1:2S RULE

11. 1:2S RULE
• One control 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

13. 1:3S RULE

14. • one control result 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
• two consecutive 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 )

16. 2:2s RULE

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 32s RULE:
• 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.

22. R4S RULE:

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

25. 31S RULE :

26. • 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.

27. 4 1S RULE :

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

31. 10 x RULE

32. • When 6 or 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.

35. 7 T RULE :

36. 7 T RULE :

37. RULE VIOLATION SYSTEMATIC ERROR RANDOM ERROR
1 : 2s
2 : 2s
1 : 3s
4: 1s
2 of 3:2s
3 : 1s
10x
7T
R : 4s

38. Within run errors
(The power 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 you do now ?

43. Corrective actions
Things that can 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

44. THANK YOU