SMILE
Johns Hopkins University
Baltimore, MD USA
Guideline Number
Westgard Rules - Guidelines
Effective Date
Author Heidi Hanes
Subject
Page
Westgard Rules Guidelines
Review by
Heidi Hanes
Review date
Pro50-10-G
12/18/06
1 of 2
1 April
2020
pSMILE Comments: This document is provided as an example only. It must be revised to accurately reflect
your lab’s specific processes and/or specific protocol requirements. Users are encouraged to ensure
compliance with local laws and study protocol policies when considering the application of this document.
If you have any questions contact SMILE.
What are Westgard Rules?
Westgard Rules are multirule QC rules to help analyze whether or not an analytical run is in-control or outof-control. It uses a combination of decision criteria, usually 5 different control rules to judge the
acceptability of an analytical run.
Westgard Rules are generally used with 2 or 4 control measurements per run, which means they are
appropriate when two different control materials are measured 1 or 2 times per material, which is the case
in many chemistries application.
For hematology, coagulations, and immunoassays applications some alternate control rules are more
suitable when three control materials are analyzed.
Explanation of Individual Rules
12s
One control measurement exceeding 2 standard deviations of control limits either above or below the mean.
This rule is used a warning rule to trigger careful inspection of the control data.
13s
This rule is commonly used with a Levey-Jennings chart when the control limits are set as the mean +3
standard deviations of control limits. A run is rejected when a single control measurement exceeds the
mean +3 control limits.
22s
The control run is rejected with 2 consecutive control measurements 2 standard deviations of control limits
on the same side of mean with this rule.
R4s
This rule rejects a run if two control measurements in a group exceed the mean with a 4 standard deviation
difference between the 2 controls
41s
This rule rejects a run with the 4th consecutive control measurement exceeding 1 standard deviation on the
same side of the mean.
10x
This rule rejects a control run when there are 10 consecutive controls on the same side of the mean.
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Johns Hopkins University
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How to perform multirule QC
To perform multirule QC collect your control measurements in the same way as you would for a regular
Levey-Jennings control chart; establish means and standard deviations for the control materials; then create
a Levey-Jennings chart with the mean +3, +2, and +1 standard deviations. The only difference is the
interpretation of the data.
The 12s rule is used as a warning to trigger application of the other rules. Any time a single measurement
exceeds a 2 standard deviation control limit, you respond by inspecting the control data using the other
rules. This doesn’t mean stop, it just means to look carefully at the data before proceeding.
By using the following diagram you should be able to decide what if any action is required.
Control Data
In-control
Report Results
12s
No
In-Control Report Results
no
Yes
no
13s
no
22s
yes
no
R4s
yes
no
41s
yes
Out-of-control, Reject analytical run
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10x
yes
yes
SMILE
Johns Hopkins University
Baltimore, MD USA
Why use a multirule QC procedure?
The advantages of multirule QC procedures are that false rejection can be kept low while at the same time
maintaining high error detection. This is done by selecting individual rules that have very low levels of
false rejection, then building up the error detection by using these rules together. It is like running two liver
function tests and diagnosing a problem if either one of them is positive. A multirule QC procedure uses
two or more statistical test, (control rules) to evaluate the QC data, and then rejects a run if any one of these
statistical tests is positive.
Other common multirules used for analyzing 3 different controls
2of32s
For this rule reject a control if 2 out of 3 control measurements exceed the same mean +2 or -2 control
limits.
31s
For this rule reject when 3 consecutive control measurements exceed the same mean +1 or -1 control limits.
6x
For this rule reject when 6 consecutive control measurements of one control fall on one side of the mean.
Reference
Westgard JO, Barry PL, Quam EF, Shrmeyer SS, Plaut D, Statland BE. Chapter 6 in Basic QC Practices,
Training in Statistical Quality Control for Healthcare Laboratories, 2 nd Edition, Westgard QC, Inc,
Madison, WI, 2002, pp77-88.
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