Interpretation of Westguard rules in clinical cemistry

7/31/2019 Interpretation of Westguard rules in clinical cemistry

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INTERPRETATION OFLEVEY-JENNINGS

CHARTS(USING LEVEY-JENNINGS

CHART TO EVALUATE RUN

QUALITY)


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The laboratory needs to document that quality

control materials are assayed and that the

quality control results have been inspected toassure the quality of the analytical run.

This is accomplished by:

Keeping QC logName of the test, the instrument, units, date,

person performing the test, results for each level

of controls, method and assay temperature.

Regular use of Levey-Jennings chart


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Levey-Jennings chart

-3

-2

-1

0

1

2

3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Run Number

Range(SD)


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-3

-2

-1

0

1

2

3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Run Number

Range(SD)

Trend Upward


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-4

-3

-2

-1

0

1

2

3

4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Run Number

Range(SD)

Shift Upward Occurred Here


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WESTGARD RULES

In 1981 Dr. James Westgard of theUniversity of Wisconsin published anarticle on laboratory quality control which

set the basis for evaluating analytical runquality for medical laboratories.

Six basic rules

These rules are used individually or incombination to evaluate the quality ofanalytical runs.


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These rules are expressed as NL

N : the number of control observations to

be evaluated

L : the statistical limit for evaluating the

control observations

13s: one control observation exceeds the

3s control limits.


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12s RULEA warning rule

A random or systematic error maybe present in the system(A single control observation is outside the 2s limit)

Patient results can be reported


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13s RULEIdentifies unacceptable random error or possibly the

beginning of a large systematic error.

(Any QC result outside 3s)

Re-test patient and QC samples


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22s RULEIdentifies systematic error only

(two consecutive QC results, greater than 2s, on the same

side of the mean)

Across run or within run


(across)


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22s RULE


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R4s RULEIdentifies random error

Applied only within current run(There is at least a 4s difference between control values

within a single run)



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31s and 41s RULEIdentifies systematic error

(3 or 4 consecutive results greater than 1s, on the same

side of the mean)Within control material or across control material

Patient results can be reported

Identifies error in a single

area of the method curve


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31s and 41s RULE

Identifies error over a broader

concentration


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10 RULE

(7 or 8, or 9, or 10, or 12 control results

On the same side of the mean regardless of the specificSD in which they are located)

Within control material or across control material

X

Identifies error in a single

area of the method curve


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SELF TEST

Rule violated 31s (Systematic error)


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13s (Randon or large systematic)


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12s Warning


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10 Systematic errorX


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None


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22s Systematic error


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13s Random or large systematic


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R4s Random error


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22s Systematic error


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Thank You

Interpretation of Westguard rules in clinical cemistry

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