Westgard rules and Sigma-based rule suggestions

Set Westgard rules for your organization, a QC lot or one analyte, and let Sigma metrics suggest a rule set, which a person applies and saves.

Each QC result is checked against Westgard rules. Legion Diagnostics supports 1-2s, 1-3s, 2-2s, R-4s, 4-1s and 10x, and each can be set to reject, warn or off.

Where rules are set

Rules are set at three levels, and each level inherits from the one above unless you customize it:

1. "Global Rules" are your organization's defaults for new QC lots (1-2s warns and 1-3s rejects unless you change them).
2. QC lot rules apply to every analyte on one lot.
3. Analyte rules apply to a single analyte. Set them with "Edit rules" at the top of the analyte. Its "Rules & targets" tab lists every rule change.

An analyte with its own rules keeps them when lot rules change; replacing them takes a deliberate overwrite. Open the rules directory under "Global Rules" to see every analyte with whether its rules are inherited or customized, its rule codes, its Sigma and who last changed it. You can download the directory as a PDF.

Sigma

Sigma describes how much room a test has before its error becomes clinically important:

Sigma = (TEa% − |bias%|) / CV%

• TEa is the analyte's total allowable error from the Test Directory.
• Bias starts at 0%, which assumes your results agree with a reference method or your peer group. You can enter a measured bias with a note saying where it came from.
• CV is never guessed. It comes from a precision study on the same control material, at least 20 days of baseline QC, or the CV measured from this lot's QC or an imported month.

Without a TEa and a CV there is no Sigma, and the current rules stay as they are.

Suggested rules

From the Sigma, Legion Diagnostics suggests a rule set for each analyte:

1-2s stays a warning and 10x stays off. Click "View evidence for rule suggestion" to see the numbers behind it.

Suggestions never change your rules on their own. Click "Apply suggestions" to load them into the rules editor, then click "Save" to put them in effect. The suggestion can tighten as soon as a little QC data shows a higher CV, but it only loosens on at least 20 measured results.

What never changes automatically

Legion Diagnostics never changes these on its own:

• the Levey-Jennings target mean and SD
• saved rules, until a person applies and saves new ones
• bias, because a shift in the QC mean is something to investigate, not a number to absorb into Sigma

Daily QC results are checked against the saved rules and targets; they do not recalculate Sigma.