Home Products Most Popular Contact
No items in your cart.
The page below is a sample from the LabCE course Introduction to Quality Control. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

Learn more about Introduction to Quality Control (online CE course) »
How to Subscribe
MLS & MLT Comprehensive CE Package
Includes 123 CE courses, most popular
$95 Add to cart
Pick Your Courses
Up to 8 CE hours
$50 Add to cart
Individual course$20 Add to cart

Westgard Multi-Rule Approach

Quality control charts are examined to see if there are problems in the measuring system. The Westgard multi-rule approach can help to determine whether there is a problem and whether that problem is due to random or systematic error.

If two controls are used, the Westgard Rules that may be considered for rejecting an analytical run are:

  • Warning Rule 12s: If one point is outside ± 2 standard deviations, this warning rule should trigger careful inspection of the data by the rejection rules listed below. If no other rules are broken, results can be accepted.
  • 13s: This rule applies when a control result falls outside of the 3s limit, either above or below the mean. The run should be rejected. Usually, this indicates that a random error has occurred.
  • 22s rule: This rule applies when two consecutive results exceed the +2 or the -2 standard deviation limit. The controls could be normal or abnormal (across runs), or one of each (within a run and both outside the same 2SD). A violation of this rule usually indicates a systematic error. The run is rejected.
  • R4s rule: This rule applies when the difference between the highest and lowest result of a run exceeds 4 standard deviations. This rule detects random errors and applies within one control level (ie, day 3 the control result falls above +2 SD and day 4 the control result falls below -2 SD) or across two control levels within one run such (ie, day 6 the high control is above +2 SD and the normal control is below -2 SD). The run is rejected.
  • 41s rule: This rule applies when four consecutive control samples all exceed the +1 or the -1 limit. The controls could be normal, abnormal, or a combination of the two. This rule detects systematic errors. The run is rejected.
  • 8x rule: This rule applies when 8 consecutive controls fall on the same side of the mean, either above or below. The rule could also apply if 4 consecutive controls fall on the same side of the mean with both controls. This rule detects a systematic error. The run is rejected.