QC - THE MULTIRULE INTERPRETATION
There are three types of errors in a Clinical Laboratory. They are
1. Crude Error [all the pre-analytical errors]
2. Random Errors [ all the sample and technical errors]
3. Systematic Errors [ its mainly from the Machine side]
How to rule out the errors?
Crude Error—it can be reduced by putting the computerization.[like the data entry and all]
Random Error—Can be checked by two Westgard rules 13s and R4s
Systematic Errors---can be checked by the following rules. 22s, 41s , 10x
The Rules:
• 13s
• 12s
• 22s
• R4s
• 41s
• 10x
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.
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.
22s - reject when 2 consecutive control measurements exceed the same mean plus 2s or the same mean minus 2s control limit.
R4s - reject when 1 control measurement in a group exceeds the mean plus 2s and another exceeds the mean minus 2s.
41s - reject when 4 consecutive control measurements exceed the same mean plus 1s or the same mean minus 1s control limit.
10x - reject when 10 consecutive control measurements fall on one side of the mean.
In addition, you will sometimes see some modifications of this last rule to make it fit more easily with Ns of 4:
8x - reject when 8 consecutive control measurements fall on one side of the mean.
12x - reject when 12 consecutive control measurements fall on one side of the mean.
In situations where 3 different control materials are being analyzed, some other control rules fit better and are easier to apply, such as:
2of32s - reject when 2 out of 3 control measurements exceed the same mean plus 2s or mean minus 2s control limit;
31s - reject when 3 consecutive control measurements exceed the same mean plus 1s or mean minus 1s control limit.
6x - reject when 6 consecutive control measurements fall on one side of the mean.
In addition, you will sometimes see some modification of this last rule to include a larger number of control measurements that still fit with an N of 3:
9x - reject when 9 consecutive control measurements fall on one side of the mean.
7T - reject when seven control measurements trend in the same direction, i.e., get progressively higher or progressively lower.
There are three types of errors in a Clinical Laboratory. They are
1. Crude Error [all the pre-analytical errors]
2. Random Errors [ all the sample and technical errors]
3. Systematic Errors [ its mainly from the Machine side]
How to rule out the errors?
Crude Error—it can be reduced by putting the computerization.[like the data entry and all]
Random Error—Can be checked by two Westgard rules 13s and R4s
Systematic Errors---can be checked by the following rules. 22s, 41s , 10x
The Rules:
• 13s
• 12s
• 22s
• R4s
• 41s
• 10x
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.
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.
22s - reject when 2 consecutive control measurements exceed the same mean plus 2s or the same mean minus 2s control limit.
R4s - reject when 1 control measurement in a group exceeds the mean plus 2s and another exceeds the mean minus 2s.
41s - reject when 4 consecutive control measurements exceed the same mean plus 1s or the same mean minus 1s control limit.
10x - reject when 10 consecutive control measurements fall on one side of the mean.
In addition, you will sometimes see some modifications of this last rule to make it fit more easily with Ns of 4:
8x - reject when 8 consecutive control measurements fall on one side of the mean.
12x - reject when 12 consecutive control measurements fall on one side of the mean.
In situations where 3 different control materials are being analyzed, some other control rules fit better and are easier to apply, such as:
2of32s - reject when 2 out of 3 control measurements exceed the same mean plus 2s or mean minus 2s control limit;
31s - reject when 3 consecutive control measurements exceed the same mean plus 1s or mean minus 1s control limit.
6x - reject when 6 consecutive control measurements fall on one side of the mean.
In addition, you will sometimes see some modification of this last rule to include a larger number of control measurements that still fit with an N of 3:
9x - reject when 9 consecutive control measurements fall on one side of the mean.
7T - reject when seven control measurements trend in the same direction, i.e., get progressively higher or progressively lower.
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