Westgard rules

westgard rules

Each laboratory should establish its own acceptance criteria for the in-laboratory control. Westgard rules come in handy, and you can implement them in a laboratory and adapt them to your needs.

There are two kinds of Westgard rules: simple and complex.

The simple ones include:

  • 13s,
  • 12S,
  • 22s,

and the complex ones:

  • 13s,
  • 41s,
  • R4s,
  • 10x.

Westgard rules – simple rules

The 12s rule – according to this principle, the method remains out of control if one result exceeds the 2 SD limit, this rule is considered a warning rule, its exceeding is a signal for the laboratory diagnostician that the quality control results should be carefully analyzed and subsequent measurements should be carefully monitored, and if necessary start action immediately.

rule 12s

Rule 13s – according to this principle, the method is out of control if one result exceeds the 3 SD limit. This rule is considered in laboratories as a method that requires action to be taken, and it is a critical rule. Exceeding this rule should suspend the performance of a given test.

Westgard rule 13s

The rules of Westguard – complex

13s – is also part of simple rules, described above

22s – method used in one series and between series.

  • in one series – two consecutive determinations in the same control material, the value of which exceeds 2 SD on the same side of the mean.
  • Between runs – two consecutive assay results in two control materials exceed 2 standard deviations on the same side of the mean.

Exceeding the 22s rule indicates a systematic understatement or overestimation of the results, and in this case, immediate action should be taken.

22s in one series

Between series:

westgard rules between series 22s

41s – the method is out of control when four consecutive results exceed one standard deviation on one side of the mean

westgard rule 41s

R4s – two results in the series outside the two standard deviations on either side of the mean – method out of control

westgard rules r4s

10x – ten results on the same side of the average, this rule is abandoned by more and more laboratories, sometimes treating it as a warning rule at best

westgard rule 10x

Unsatisfactory results of the intra-laboratory control – activities

Examples of actions carried out in the event of a violation of the above rules:

  • duplicating the control with the same sample
  • Repeating the control from a fresh sample (this is the same material reconstitution or a new one)
  • calibrating the test and carrying out checks (the correctness of the calibration should always be confirmed by performing an intra-laboratory check at all available levels)
  • check the LOT number of the calibrator and the entered calibrator values
  • verification of the control LOT number and entered control values
  • check for updates of calibrator and control leaflets
  • carrying out the cleaning procedures of the analyzers
  • reagent replacement
  • in the case of lyophilized controls and calibrators, checking of automatic pipettes
  • call for technical service

In fact, it is difficult to determine which of the above actions should be performed in a particular case. It all depends on the type of test, the stability of the reagent, calibrator or control. Working with a specific analytical system, we work out the shortest way to obtain satisfactory results of intra-laboratory quality control and ensure reliable results of our tests.

Below we present the Westguard Rules test and the principles of intra-laboratory control. We hope you will solve it flawlessly! We also invite you to discuss in the comments.

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Disclaimer: This page is for informational purposes only. Conversion rates have been compiled based on publicly available information. All information should be confirmed and verified. The data on the site is not a substitute for professional medical advice. Any information, result, conversion should be consulted with a doctor.

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