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Levey-Jennings Chart

A graphical method for displaying control results and evaluating whether a procedure is in-control or out-of-control
Control values are plotted versus time
Lines are drawn from point to point to accent any trends, shifts, or random excursions


Findings Over Time
Ideally should have control values clustered about the mean (+/-2 SD) with little variation in the upward or downward direction
Imprecision = large amount of scatter about the mean. Usually caused by errors in technique
Inaccuracy = may see as a trend or a shift, usually caused by change in the testing process
Random error = no pattern. Usually poor technique, malfunctioning equipment


Statistical Quality Control Exercise

Hypothetical control values (2 levels of control)
Calculation of mean
Calculation of standard deviation
Creation of a Levey-Jennings chart



Westgard Rules chart
“Multirule Quality Control”
Uses a combination of decision criteria or control rules
Allows determination of whether an analytical run is “in-control” or “out-of-control
The formulation of Westgard rules were based on statistical methods. Westgard rules are commonly used to analyse data in Shewhart control charts.
Westgard rules are used to define specific performance limits for a particular assay and can be use to detect both random and systematic errors.
There are six commonly used Westgard rules of which three are warning rules and the other three mandatory rules.
The violation of warning rules should trigger a review of test procedures, reagent performance and equipment calibration.
The violation of mandatory rules should result in the rejection of the results obtained with patients’ serum samples in that assay.
(Generally used where 2 levels of control material are analyzed per run)
warning rule”
One of two control results falls outside ±2SD
Alerts tech to possible problems
Not cause for rejecting a run
Must then evaluate the 13S rule


Shewhart Control Charts
A Shewhart Control Chart depend on the use of IQC specimens and is developed in the following manner:-
Put up the IQC specimen for at least 20 or more assay runs and record down the O.D./cut-off value or antibody titre (whichever is applicable).
Calculate the mean and standard deviations (s.d.)
Make a plot with the assay run on the x-axis, and O.D./cut-off or antibody titre on the y axis.
Draw the following lines across the y-axis: mean, -3, -2, -2, 1, 2, and 3 s.d.
Plot the O.D./cut-off obtained for the IQC specimen for subsequent assay runs
Major events such as changes in the batch no. of the kit and instruments used should be recorded on the chart.



Mandatory rules
Mandatory 13SD : It is violated when the IQC value exceeds the mean by 3SD. The assay run is regarded as out of control.

Mandatory R4SD : It is only applied when the IQC is tested in duplicate. This rule is violated when the difference in SD between the duplicates exceeds 4SD.

Mandatory 10x : This rule is violated when the last 10 consecutive IQC values are on the same side of the mean or target value.