lab quality control and assurance, westgard rule

1. QUALITY ASSURANCE IN CLINICAL
LAB
DR NIDHI RAI

2. INTRODUCTION
 definition
Aims & objectives
Quality assurance vs quality control : is it the same?
Definitions :
Components of quality assurance
Application in lab testing
Accreditation & Certification

3. QUALITY ASSURANCE : DEFINITION
 “All steps taken by the director of the
laboratory to ensure reliability of lab results &
increase accuracy, precision & laboratory
comparability”
Aims
Minimize
variability in
results arising
from these
sources
Ensure the
reliability of
investigations

4. The Quality Assurance Cycle
•Data and Lab
Management
•Safety
•Customer
Service
Patient/Client Prep
Sample Collection
Sample Receipt
and Accessioning
Sample Transport
Quality
Control
Record Keeping
Reporting
Personnel Competency
Test Evaluations
Pre- analytical
Analytical
Post- analytical

5. Quality assurance
Quality control of
all phases of testing
from sample collection
to delivery of reports
Inclusive of quality
control
Quality control
Control of a specific
process in testing-
generally analytical
phase.
Component of quality
assurance

6. COMPONENTS OF QUALITY ASSURANCE
Internal
quality control
Proficiency
surveillance
External
quality
assessment

7. QUALITY ASSURANCE IN HEMATOLOGY LAB
CONTROL OF
PHASES
EXTERNAL QUALITY
ASSESSMENT (EQA)
PROFICIENCY
SURVEILLANCE
1. PRE- ANALYTICAL
PHASE
 Errors : 60-70%

8. “ A TEST IS ONLY AS GOOD AS THE QUALITY OF THE SPECIMEN”
pt identification
& requisition
Pt preparation &
Sample collection
•Information
•Details of test
l
• tourniquet application
•Site
•Improper mixing
•Time of draw
•Pt condition
Sample transport &
storage
•Labeling
• refrigeration
Training of
personnel

9. QUALITY ASSURANCE IN HEMATOLOGY LAB
CONTROL OF
PHASES
EXTERNAL QUALITY
ASSESSMENT (EQA)
PROFICIENCY
SURVEILLANCE
1. PRE- ANALYTICAL
PHASE
 Errors : 60-70%
ANALYTICAL
PHASE/ IQC
 Errors: 5-15%

10. CONTROL OF ANALYTICAL PHASE
SOP & REAGENTS
MAINTENANCE OF NEW
INSTRUMENTS &
CALIBRATION
DETERMINE UOM &
LINEARITY
REFERENCE RANGE
DETERMINATION
PERSONNEL
REQUIREMENTS &
COMPETENCY TESTING
CONTINUING
EDUCATION
INTRODUCE QUALITY
CONTROL

11. A. STANDARD DEVIATION :
Mean ( x ) the total score of all the measurements
divided by the number of measurements
 Standard deviation ( SD ) – variation in measurement
obtained in lab tests
formula: SD = Σ ( x – x )2
n – 1
n : number of observations
 If value is between 2 S.D and 3 S.D----warning range.
*2 S.D.--- Warning limit
3 S.D--- alarm limit.
Imprecision expressed as S.D
IQC

12.  Coefficient of variation (CV) / relative S.D:
 used to compare the precision of results over a wide
range values when S.D would vary considerably.
C.V= S.D *100 %
x’
 < 3% ---ideal
 3% ---acceptable
 CV is relation of SD to the actual measurement
IQC

13. COMPONENTS OF QUALITY ASSURANCE
 INTERNAL QUALITY CONTROL (IQC)
 continual assessment of day to day work carried
out, evaluation of results of tests done to decide
their reliability.
IQC
Precision
Linearity
Accuracy
Aims :

14. DEFINITION OF TERMS USED IN QA
 PRECISION :
 closeness with which
repeat measurements
on one sample agree.
May or may not be
accurate
ACCURACY:
 measure of closeness
of an estimated value
to the true value.
Closer the value to
actual value, more
accurate it is
Data can be very precise but inaccurate

15. PRECISION & ACCURACY
ACCURATE & PRECISE
-RESULTS

16. PRECISION & ACCURACY
ACCURATE BUT NOT PRECISE
-RESULTS

17. PRECISION & ACCURACY
PRECISE BUT NOT ACCURATE
-RESULTS

18. PRECISION & ACCURACY
NEITHER ACCURATE NOR PRECISE
-RESULTS

19. DEFINITION
Repeatability refers
ability of a
test/experiment to
be accurately
reproduced by the
same person
Reproducibility
refers the ability of
a test/ experiment to
be accurately
reproduced by
someone else working
independently.
PRECISION
While repeatability is desirable ; it is limited by practicability

20. QUALITY ASSURANCE IN HEMATOLOGY LAB
1. PRE- ANALYTICAL
PHASE
 Errors : 60-70% ANALYTICAL
PHASE/ IQC
 Errors: 5-15%
A. TESTING FOR
PRECISION
B. TESTING FOR
ACCURACY

21. A. TESTING FOR PRECISION:
1. QC USING CONTROL SAMPLES
 At least one control / batch of specimen to be
analysed.
Large batch : 1 control/ 20 pt specimens.
Use methods of dispersion
eg: SD, CV
Prepare control charts
IQC

22. IQC
Control
charts
CUSUM
Westgard
Rule
Tests for
precision

23. A. CONTROL CHARTS
 Described by Shewhart, applied by Levey &
Jennings.
 Samples of the control sp are plotted on control
chart
 To check precision, it is not needed to know the
exact value of the control sp.
IQC

24. 0
10
20
30
40
50
60
70
80
90
100
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
LJ CONTROL CHART
+3 sd
-3 sd
+2 sd
-2 sd
-1 sd
+1 sd
Target value
time -x axis (run)
Y
r
e
p
v
al
u
e
IQC

25.  One widely deviant result outside 3 S.D
GROSS ERROR.
 2 or more results on or outside 2 S.D
RANDOM ERROR.
 Several consecutive values on one side of mean
CALIBERATION FAULT.
 Consecutive values constantly rising or falling
CONTINUING BIAS/ ERROR.
INTERPRETATION
IQC

26. TYPES OF SYSTEMIC ERRORS:
Inaccurate but precise – systemic error
Shift: Abrupt change in the control mean.
A sudden and dramatic change positive or negative
change in test system performance.
Trend: gradual loss of reliability in the test system.

27. IQC

28. CAUSES OF SHIFT:
1. Light source
2. Reagent formulation
3. Major instrument Maintenance
4. Room temp
5. Failure in the sampling system/reagent
dispensing change in reagent formulation lot
6. Major instrument maintenance/change in room
temp or humidity
7. Failure in the reagent dispense/inaccurate
calibration or recalibration

29. CAUSES OF TREND:
1. Deterioration of the instrument light source
2. Gradual accumulation of debris in sample
reagent tubing.
3. Aging of reagents
4. Gradual deterioration of control materials.
5. Gradual deterioration of incubation chamber
temperature
6. Gradual deterioration of calibration

30. RANDOM ERROR
 Impression computed as random error
 A random deviation from an expected result
Causes:
1. Improperly mixed/dissolved reagents.
2. Airbubbles in reagents and reagents
lines,sampling or reagent syringes
3. Pipette tips is not fitting properly
4. A clogged pippetor (Clot)
5. Unstable temp and incubation
6. Unstable power supplu

31. CAUSES OF RANDOM ERROR CONTINUE:
7. Poor operator techniques
8. Improper mixing of processed samples.
9. Incorrect reconstitution of the control
material.

32.  Westgard has formulated rules to decide
whether an analytical run in in cotrol or out of
control.
 These rules can be applied as single rules and as
group of rules(multi rules)
 Applied only if QC are plaotted with the range of
3 SD.
WESTGARD RULES:
IQC

33. RULES FOR WHAT?
 Two key factors to keep in mind while
selecting/using rules are:
 Maximize error detection:
Per cent error detection (P ed) > 90%
 Minimize False Rejection:
Percent False rejection ( P fr) <5%

34.  While talking about QC rules nomenclatures we
have to understand 2 sets of nomenclatures
1. N and L
2. Within/across the run/material

35. CONTROL RULE NOMENCLATURE 1:
N:L
N :Number of control measurements involved
L: Limit exceeded

36. CONTROL RUN NOMENCLATURE 2:
 With-run/Across material: At 2/3 levels of QC
in the same run
 Across run/Within material: same level of QC
but in 2 or consecutive run.
Date QC levels
Day 1 Level 1 Level 2 Level 3
Day 2 Level 1 Level 2 Level 3
Day 3 Level 1 Level 2 Level 3
Day QC levels
Day 1 Level 1 Level 2 Level 3
Day 2 Level 1 Level 2 Level 3
Day 3 Level 1 Level 2 Level 3

37. WESTGARD RULES:
 12S rule
 13S rule
 22S rule
 R4S rule
 41S rule
 10X rule

38. WESTGARD – 1 2S RULE
 “warning rule” Denotes a random error or the
beginning of a systemic error
 One of two control results falls outside ±2SD
 Not cause for rejecting a run.
 Important : If only one level of QC is being run
in the lab,1:2S has to be rejection rule.
IQC

39. 12S RULE = A WARNING TO TRIGGER CAREFUL
INSPECTION OF THE CONTROL DATA
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Mean
Day
+1SD
+2SD
+3SD
-1SD
-2SD
-3SD
12S rule
violation
IQC

40. WESTGARD – 13S RULE
 If either of control results falls outside of
±3SD, rule is violated
 Denotes a random error or beginning of a large
systemic error.
 Run must be rejected
 If 13S not violated, check 22S
IQC

41. 13S RULE = REJECT THE RUN WHEN A SINGLE
CONTROL MEASUREMENT EXCEEDS THE +3SD OR -3SD
CONTROL LIMIT
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Mean
Day
+1SD
+2SD
+3SD
-1SD
-2SD
-3SD
13S rule
violation
IQC

42. WESTGARD – 22S RULE
 2 consecutive control values for the same level
fall outside of ±2SD in the same direction(across
the run) or
 Both controls in the same run exceed ±2SD
(within run).
 This rule identifies systemic error only.
 Requires corrective action
IQC

43. EXAMPLE OF 2:2S
 If a normal (level 1)and abnormal (level II) control
are
 >2S on the same side of the mean
 This run violates the within run application for
systemic error.
o If However, level I is acceptable and Level II is
1:2S,the level II result from the previous run must
be examined.
o If Level II in the previous run was
 At +2.00 S or greater
 Then the across run application for systematic error
is violated.

44. 22S RULE = REJECT THE RUN WHEN 2 CONSECUTIVE
CONTROL MEASUREMENTS EXCEED THE SAME +2SD OR -
2SD CONTROL LIMIT
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Mean
Day
+1SD
+2SD
+3SD
-1SD
-2SD
-3SD
22S rule
violation
IQC

45. WESTGARD – R4S RULE
 One control exceeds the mean by –2SD, and the
other control exceeds the mean by +2SD
 The range between the two results will
therefore exceed 4 SD
 This test should only be interpreted within run
,not across run..
 Random error has occurred, test run must be
rejected
IQC

46. R4S RULE = REJECT THE RUN WHEN 1
CONTROL MEASUREMENT EXCEED THE +2SD AND
THE OTHER EXCEEDS THE -2SD CONTROL LIMIT
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Mean
Day
+1SD
+2SD
+3SD
-1SD
-2SD
-3SD
R4S rule
violation
+1SD
IQC

47. WESTGARD – 41S RULE
 Requires control data from previous runs
 Four consecutive QC results for one level of
control are outside ±1SD, or
 Both levels of control have consecutive results
that are outside ±1SD
IQC

48. WESTGARD – 10X RULE
 Requires control data from previous runs
 Ten consecutive QC results for one level of
control are on one side of the mean, or
 Both levels of control have five consecutive
results that are on the same side of the mean
IQC

49. Rules Violation Systemic Error Random Error
1:2S + +
2:2S +
1:3S + +
4:1S +
10X +
R4S +

50. QC Data
12S
13S 41S
R4S
22S 10x
Report Results
Take corrective action
Flowchart and logic for the multi-
rule internal quality control (IQC)
procedure commonly known as
‘Westgard rules’
IQC

51. QUALITY ASSURANCE IN HEMATOLOGY LAB
1. PRE- ANALYTICAL
PHASE
 Errors : 60-70% ANALYTICAL
PHASE/ IQC
 Errors: 5-15%
A. TESTING FOR
PRECISION
B. TESTING FOR
ACCURACY

52. QUALITY ASSURANCE IN HEMATOLOGY LAB
CONTROL OF
PHASES
EXTERNAL QUALITY
ASSESSMENT (EQA)
PROFICIENCY
SURVEILLANCE
1. PRE- ANALYTICAL
PHASE
 Errors : 60-70%
ANALYTICAL
PHASE/ IQC
 Errors: 5-15%
POST- ANALYTICAL
PHASE
Errors : 10-15%

53. POST- ANALYTICAL PHASE:
 review of pt results.
 Posting pt results after checking for reliability
 Highlighting abnormal results
 Effective information conveyed to requester
 Maintaining patient records
 Maintaining all documentation
1. errors while testing
2. spillage of samples
3. internal & external complaint register
 monitoring of turnaround time ( TAT)

54.  Purpose – to achieve harmonization concordance b/w labs
 Principle: same material is sent from a national or regional
centre to a large number of laboratories
 All the labs send the results back to the centre where
they are analyzed and interpreted by one of several
procedures
 From the results returned from the participants, the
median or mean and SD are calculated
 An individual lab can then compare its performance in the
survey with that of other labs and with its own previous
performance ( using deviation index )
EXTERNAL QUALITY ASSESSMENT:

55.  A deviation index ( score ) =
actual results – weighted mean for test
weighted SD
Interpretation :
0.5 – excellent
0.5-1.0 – satisfactory
1.0- 2.0 – acceptable
> 2.0 – defect requiring attention
EQA

56. REFERENCES :
 Quality assurance with special reference to
hematology : Dr. SOOD ;
Sir Ganga Ram Hospital , New Delhi
 Shirlyn McKenzie : textbook of hematology
 Dacie & Lewis
 Quality assurance – working manual .

57. THANK YOU