This free Westgard rules checker plots your QC data on a Levey-Jennings chart and flags every rule violation. Paste your control results in time order, enter the target mean and SD, and the tool plots a Levey-Jennings chart and checks every point against the Westgard multirules. It flags warnings and rejections so you can decide whether to accept the run.
How to use the Westgard Rules Checker
- Enter the target mean and target SD for the control material, or let the tool calculate them from your data.
- Paste QC results in time order, oldest first.
- Press Check Westgard rules.
- Read the Levey-Jennings chart and the list of violated rules, then accept or reject the run.
Use the Westgard rules checker on each control level separately unless your SOP applies rules across levels. The full multirule procedure is explained by Westgard QC.
The Westgard multirules explained
| Rule | Triggered when | Detects | Action |
|---|---|---|---|
| 1-2s | One result beyond ±2 SD | Warning only | Inspect with the other rules |
| 1-3s | One result beyond ±3 SD | Random error | Reject run |
| 2-2s | Two consecutive results beyond 2 SD on the same side | Systematic error | Reject run |
| R-4s | One result above +2 SD and the next below −2 SD (range > 4 SD) | Random error | Reject run |
| 4-1s | Four consecutive results beyond 1 SD on the same side | Systematic shift | Reject, or recalibrate |
| 10x | Ten consecutive results on the same side of the mean | Bias or drift | Reject, or investigate |
This checker applies the rules to a single control material across consecutive runs. If you run two control levels per run, check each level here and also compare them within the run (for example a 2-2s across both levels).
Setting the mean and SD
- Establish the target mean and SD from at least 20 in-control runs on your own system, not the manufacturer’s insert range.
- Recalculate after reagent lot changes, major maintenance or recalibration.
- For chemistry labs outside clinical settings, the same approach works as a Shewhart control chart for check standards, reference materials and duplicates.
Frequently asked questions
Is a 1-2s violation a reason to reject a run?
No. In the classic Westgard scheme 1-2s is only a warning that triggers checking the other rules. Rejecting on 1-2s alone causes too many false rejections (about 5% of runs for one control, about 9% for two).
Which Westgard rules detect systematic error?
2-2s, 4-1s and 10x detect systematic error (shifts and trends). 1-3s and R-4s mainly detect random error.
How many QC points do I need to set up a Levey-Jennings chart?
At least 20 data points from separate runs is the usual minimum for establishing a reliable mean and SD.
Can I use this for ISO/IEC 17025 chemistry labs?
Yes. Control charts for check standards or reference materials are a common way to meet the result-validity monitoring requirement of clause 7.7.
How do you read a Levey-Jennings chart?
Each QC result is plotted in time order against lines at the mean, ±1 SD, ±2 SD and ±3 SD. Points outside ±3 SD, runs of points on one side of the mean, or a steady drift point to random or systematic error.
Can you give a Westgard rules example?
Say the mean is 100 and the SD is 2. A result of 107 is more than 3 SD from the mean, which breaks 1-3s and rejects the run. Two consecutive results of 104.5 and 105 are both beyond +2 SD, which breaks 2-2s and points to a systematic shift.
When should I update the Levey-Jennings chart limits?
Review the mean and SD when you change reagent or control lots, after major maintenance, and at least every few months. Base new limits on 20 or more in-control results collected over several runs.
Related tools
Results are estimates for general information. Check critical decisions with a qualified professional.