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The 22s rule detects systematic error only. The 22s rule is violated when two consecutive QC results are:
The rule is applied both within a run and across runs:
Two control values in the same run are >2SD on the same side of the mean. Violation of the within run application indicates systematic error is present and potentially affecting the entire analytical curve.
In one run a single level of control is >2SD from the mean. In the next run, the same level of control is >2SD on the same side of the mean. Violation of the across run application indicates systematic error is present but affects only a single portion of the analytical curve.
The following figures show a Levey-Jennings Chart with a data point violating the 22s rule within and across a run.
Within run violation
Across run violation
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