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.

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.

Molecular Diagnostic QC?

Originally posted on October 3rd, 2006.

We don't often talk about molecular diagnostics and quality control. Getting a handle on the "usual" tests in chemistry, hematology, etc., has been a tough enough job. But the field of molecular diagnostics is expanding rapidly. And quality for those tests is going to be just as important, if not more important in the future.

 
Here's a simple description of a quality issue in molecular diagnostics testing: picture a tube or a well, or in the case of multiplex testing, several tubes or an array of wells. Each entity contains several different reactions to determine the presence or absence of specific genetic sequences. The current practice is to test just one or two of the reactions for quality control. And even if the QC reaction has different detection probes or primers than all the others reactions, if the value for the control is "in", it is assumed that all of the other results are valid.

 
This has been the state of the art for a limited number of assays and it seems risky at best. But these array tests are growing by orders of magnitude. Where now there may be under 100 tests in an array, new ones that will have several hundred, maybe a thousand, are under development. The validity of the current state of the art for QC, that is, to rely on testing just a small sampling of the different reactions, needs to be examined.

 
Dr. Clark Rundell, from Maine Molecular Diagnostics, is at the forefront of the QC field for molecular diagnostics. He recently wrote an article for MLO on the "QC challenges for molecular testing." It's worth a look - this is going to be one of the key early articles for this important area.

http://www.mlo-online.com/articles/0506/0506special_feature.pdf

Permission given by Medical Laboratory Observer, May 2006
Copyright (symbol) 2006 by Nelson Publishing Inc *www.mlo-online.com

Update on QC Design Tools

Originally posted June 20, 2008

Just a short note to point out a new

essay

on QC Design tools that we've posted.

As I tell people who attend the workshops, you can't just listen to the theory of QC Design. You've got to go back to your laboratories and try it yourself.

Over the years, I've been a part of many teams that developed QC Design tools. Every new tool seems to get better, more sophisticated, and yet easier to use. The ultimate goal is to give you a powerful tool that you can use with minimal effort.

Read the essay and come back here to make comments.