The Westgard Rules

Sigma metrics in veterinary testing

By Sten Westgard, MS

I just wanted to draw your attention to a seminal paper that came out recently:

Quality control validation, application of sigma metrics, and performance comparison between two biochemistry analyzers in a commercial veterinary laboratory, Alison J Farr and Kathleen P Freeman, J Vet Diagn Invest. September 2008;20(5):536-44. (subscription required)

In this paper, Kathy Freeman, who has previously written a guest essay for Westgard Web, and her colleague Alison Farr apply Sigma metrics and QC design to common veterinary diagnostic tests. QC in veterinary testing is not a subject that is well covered in the scientific literature.

What's most interesting from our point of view is that in order to calculate Sigma metrics and perform QC Design on these tests, Freeman and Farr needed key information: quality requirements for veterinary tests for the major non-human species (cat, dog, horse). For the most part, the requirements don't exist, or at least a set of goals is not in widespread circulation. So Freeman and Farr did a survey review and made some assessments of test interpretation in their own laboratory. The result is the largest list of quality requirements for veterinary testing that we've ever seen. We excerpted the table, with Freeman's permission, here. 

It's a comprehensive paper, covering the method principles, decision levels, quality requirements, Sigma metrics, and QC Design with rule implementation. Highly recommended.

What's New: November 2008

New Download: Sigma-Metrics Tool (and audioconference presentation)

On September 4th, 2008, Dr. Westgard spoke as part of the AACC audioconference on "New Directions in Laboratory QC" -  which was subsequently quoted in the Clin Lab News article on Risk and CLIA.  We are pleased to make available Dr. Westgard's complete presentation, as well as two Sigma-metrics Charts and instructions on how to use them in QC Design.

http://www.westgard.com/audiodownload.html

Westgard Sigma Analysis: A new direct HbA1c Method

At the 2008 AACC/ASCLS convention, a poster was presented for a new direct enzymatic assay for %HbA1c. How does it stack up against HPLC and immunoassay methods? How do you judge a method when you've got multiple comparison methods and multiple quality requirements?

http://www.westgard.com/qcapp53.htm

Interview: Dr. R. Neill Carey (A brief introduction to EP 15)

We were fortunate to get R. Neill Carey, PhD, the chair of the CLSI EP 15 committee, to present and 

explain that new standard at the Chicago Method Validation workshop. He also contributed a chapter to the new Basic Method Validation manual on the same topic. But for those who have never heard of EP 15 before, we conducted a short interview with Dr. Carey. This short introduction to EP 15 may pique your interest in this new guideline.

http://www.westgard.com/interview9.htm

Thinking about Three Sigma: 2 thoughts on troublesome performance

In a previous lesson, we discussed some possible actions to take when the Sigma-metric for a method is higher than Six. But what about those methods with low Sigma-metrics? What do you do when Sigma analysis delivers bad news?

http://www.westgard.com/lesson87.htm

c8000 Sigma Analysis

Posted by Sten Westgard

One of the highlights for me of the AACC convention in Washington, DC, was my inclusion in a poster that analyzed the method performance of the Abbott Architect c8000. I'm pictured here with fellow authors (left to right) Gene Osikowicz, Charles Wilson, and John Baker (lead author). They deserve most of the credit for the work of collecting the data.

The poster can be viewed here and the QC application on Westgard Web can be viewed here.