Posted by Sten Westgard, MS
An online-first paper just came to our attention, a study that used Sigma-metrics and the Six Sigma Cost Worksheets included in our book:
Use of Six Sigma Worksheets for assessment of internal and external failure costs associated with candidate quality control rules for an ADVIA 120 hematology analyzer. Cian F1, Villiers E, Archer J, Pitorri F, Freeman K. Vet Clin Pathol. 2014 Apr 21. doi: 10.1111/vcp.12141. [Epub ahead of print]
This new study applied Sigma-metrics to hematology tests, but used a different set of quality requirements more appropriate for veterinary uses. This is interesting to see, since the differences between the CLIA requirements for hematology (for humans) are sometimes half or a third of what is being used for veterinary uses (dogs, cats, etc.). So what might not be a great method for humans could be a world class method for dogs!
The authors estimated the savings for changing from 1:2s rule with N=3 (their current practice, and one with a high false rejection rate) just to the 1:2.5s rule with N=3. Even that slight change created a 72% reduction in QC usage, saving about £822 a year. That doesn't seem like much, admittedly, but this a lab with relatively small volume: about 30 CBCs a day, 9000 CBCs annually. That Six Sigma techniques can save money for the lower volume vet lab and the higher volume human reference lab is a good sign of universal utility.
This savings is also assuming that only control costs are taken into account - that even when rejections occur, no patients are re-run, only the controls. If the lab policy was to re-running all the patients whenever there was a rejection flag, the savings would be an order of magnitude higher.
Congrats to this veterinary lab, for applying a technique that many (human) labs are still lagging in adoption.