QC THE MULTIRULE INTERPRETATION

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QC THE MULTIRULE INTERPRETATION
Chemometrics
Department of Chemical Pathology, University of
Pretoria,
Dr R Delport 2003
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Chemometrics
Multirule QC uses a combination of decision
criteria, or control rules, to decide whether an
analytical run is in-control or out-of-control.
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Chemometrics
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.
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Chemometrics
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.
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Chemometrics
22s - reject when 2 consecutive control
measurements exceed the same mean plus 2s or the
same mean minus 2s control limit.
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Chemometrics
R4s - reject when 1 control measurement in a
group exceeds the mean plus 2s and another
exceeds the mean minus 2s.
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Chemometrics
41s - reject when 4 consecutive control
measurements exceed the same mean plus 1s or the
same mean minus 1s control limit. 
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Chemometrics
10x - reject when 10 consecutive control
measurements fall on one side of the mean.
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Chemometrics
8x - reject when 8 consecutive control
measurements fall on one side of the mean.
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Chemometrics
12x - reject when 12 consecutive control
measurements fall on one side of the mean.
The preceding control rules are usually used with
N's of 2 or 4, which means they are appropriate
when two different control materials are measured
1 or 2 times per material.
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Chemometrics
In situations where 3 different control materials
are being analyzed
2of32s - reject when 2 out of 3 control
measurements exceed the same mean plus 2s or mean
minus 2s control limit
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Chemometrics
31s - reject when 3 consecutive control
measurements exceed the same mean plus 1s or mean
minus 1s control limit.
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Chemometrics
6x - reject when 6 consecutive control
measurements fall on one side of the mean. 
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Chemometrics
9x - reject when 9 consecutive control
measurements fall on one side of the mean. 
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Chemometrics
A related control rule that is sometimes used,
particularly in Europe, looks for a "trend" where
several control measurements in a row are
increasing or decreasing
7T - reject when seven control measurements trend
in the same direction, i.e., get progressively
higher or progressively lower.
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Chemometrics

• False alarms are minimized by using the 12s rule
  as a warning rule, then confirming any problems
  by application of more specific rules that have a
  low probability of false rejection (serial
  testing).
• True alarms or error detection are maximized by
  selecting a combination of the rules most
  sensitive to detection of random and systematic
  errors, then rejecting a run if any one of these
  rules is violated (parallel testing).

http//www.westgard.com/lesson3.htm QC - THE
PLANNING PROCESS
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Chemometrics
The key in how to apply control rules with
multiple materials and multiple runs is to
identify which control results represent
consecutive measurements e.g., if one
measurement is made on each of two different
control materials in an analytical run, control
rules can be applied as follows

• The two control results "within a run" can be
  inspected by applying a 13s rule to each
  material, as well as the 22s and R4s rules
  "across materials."
• The 22s rule can also be applied to the last two
  measurements "within a material and across runs."
  
• The 41s rule can be applied to the two control
  measurements in the current run and the two
  measurements in the previous run, i.e., the rule
  can be applied "across materials and across
  runs".
• The 41s rule can also be applied to the last four
  measurements "within a material and across runs,"
  which now requires the control results from the
  three previous runs.
• The 10x rule can be applied to both control
  measurement in a run for the last five runs, or
  to the measurements on just one material for the
  last ten runs.

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Chemometrics
Because of these many possible applications of
individual rules in a multirule QC procedure, it
is best to provide specific directions for when
to analyze controls, how to interpret the
results, and what to do based on those results.

1. Statistical QC procedure. Use a 12s warning rule
   and the 13s/22s/R4s/41s/10x rejection rules with
   2 control measurements per run.
2. Analysis of control materials. Analyze one sample
   of the Level A control and one sample of the
   Level B control in each run.
3. Interpretation of warning rule. If both control
   results are within 2s limits, report the patient
   test results. If one control result exceeds a 2s
   limit, inspect the control data as follows and
   reject the run if any control rule is violated

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Chemometrics
4. Within run inspection of control results.
Inspect the control results in the current run by
applying the 13s rule to the results from each
material and the 22s and R4s rules across
materials. Note that the 41s and 10x control
rules cannot be applied within a run because
there are only two control measurements
available. 5. Across run inspection of control
results. Apply the 22s rule within each material
across the last two runs apply the 41s rule
within each material across the last 4 runs
apply the 41s rule across the last two runs and
the two measurements on each material apply the
10x rule across the last five runs and the two
measurements on each material. Note that this
protocol does not specify applying the 10x rule
within each material across the last ten runs.
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Chemometrics
6. Interpretation of rejection rules. If none of
the rules in steps 3 and 4 are violated, accept
the run and report patient results. If any one of
the rules in steps 3 and 4 is violated, the run
is out-of-control do not report patient test
results. 7. Problem-solving. When a run is
out-of-control, investigate the process and
correct the problem, in the following way

1. Determine the type of error occurring on the
   basis of the rule violated. Random error is
   usually indicated by the 13s or R4s rules,
   whereas systematic error is more likely indicated
   by the 22s,41s, or 10x rules.
2. Refer to trouble-shooting guides to identify
   possible causes for the type of error indicated
   by the control rule that was violated.
3. Inspect the testing process and identify the
   cause of the problem.
4. Correct the problem, then analyze control samples
   again to assess control status.
5. Repeat or verify the results on the patient
   samples once the method has been demonstrated to
   be in-control.
6. Consult a supervisor for any decision to report
   patient results when a run is out-of-control.

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Chemometrics
Example control results for this multiple rule
application
High mean250 and s5)
Low mean200 and s4
Identify the rule at 3,4,7,9,10, 11,12,14,20
http//www.westgard.com/lesson18.htmterminology
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Chemometrics
Run 3 Both control results exceed their
respective 2s limits, therefore there is a 22s
rule violation across materials. A systematic
error is most likely occurring and is affecting
the results throughout the critical analytical
range from at least 200 to 250 mg/dL.
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Chemometrics
Run 4 The high control result is below its -2s
limit, which is a warning of a possible problem.
Inspection with the 13s, 22s, and R4s rejection
rules that can be applied within the run do not
confirm a problem. Note that the across-runs
rules would not be applied because the previous
run was rejected.
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Chemometrics
Run 7 The high control result exceeds its 3s
limit, therefore there is a 13s control rule
violation. This most likely indicates random
error.
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Chemometrics
Run 9 The high control result is below its -2s
limit. Inspection of the control results by the
rejection rules does not confirm a problem.
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Chemometrics
Run 10 The control chart for the high control
material shows that the last two measurements
have both exceeded the -2s limit, therefore a 22s
rule violation has occurred within material and
across runs. This situation would be consistent
with a loss of linearity that is beginning to
affect the high end of the analytical range.
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Chemometrics
Run 11 There is a 12s warning on the high level
control material, but inspection doesn't show any
other rule violations, therefore, the patient
test results in this run can be reported.
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Chemometrics
Run 12 The control charts for the high and low
materials show that the last four control
observations have exeeded their respective 1s
limits, therefore a 41s rule violation appears to
have occured across materials and across runs.
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Chemometrics
Run 12 Note, however, that the QC protocol
specified that a control result had to first
exceed a 2s control limit before initiating the
application of the 41s rule. Therefore,
according to the protocol, this run would not be
interpreted as out-of-control.
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Chemometrics

Run 14 The control results for the high material
exceeds its 2s limit and the control result for
the low material exceeds its -2s limit, therefore
an R4s rule violation has occurred. This most
likely indicates a random error.
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Chemometrics

Run 14 The control results for the high material
exceeds its 2s limit and the control result for
the low material exceeds its -2s limit, therefore
an R4s rule violation has occurred. This most
likely indicates a random error.
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Chemometrics

Run 20 The last five control results on the high
material and the last five results on the low
material all are lower than their respective
means, giving a total of ten consecutive control
results on one side of the mean. There is a 10x
rule violation across runs and across materials,
which indicates that a systematic error most
likely has occurred.
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Chemometrics
QC - THE LEVEY-JENNINGS CONTROL CHART
Exercise http//www.westgard.com/lesson12.htm
Answer http//www.westgard.com/lssn12p2.htm