Six Sigma

A recent study detailed the benefits of applying the Sigma-metric approach. They assess analytical Sigma-metrics before, performed improvements, and then re-assessed the Sigma-metrics after. Can you guess how much improvement they experienced?

 Benefits of Sigma-metric implementation: identifying quality interventions, training, and enhancing performance

December 2024
Sten Westgard, MS

[Sigma scoring: 3rd party controls, over intermediate reproduciblity conditions, with controls near medical decision levels, comparison against peer group/EQA, over multiple surveys = Moderate quality study]

Recently, there have been objections raised about the usefulness of the Six Sigma model in laboratory medicine. It's been claimed there are no benefits to application of the analytical Sigma-metric. Here's a simple rebuttal. Sigma-metrics help methods get better.

Our study of interest was published this month, December 2024:

Application of Six Sigma Metrics for assessing the quality management of biochemical analytes in the clinical laboratory. Saurabh Singh, Manisha Singh, Devesh Sharma, Ijen Bhattacharya, Mamta Padhy, Surabhi Puri, Utkarsh Singh Tomar. Asian Journal of Medical Sciences, December 2025, Volume 15, Issue 12, 70-78.

 This study is unique in that it's one of the first studies to use CLIA 2024/5 benchmarks, and it is one of the rare birds where there are before and after metrics. That is, preliminary Sigma-metrics were calculated, something was done to improve the methods, and then subsequent Sigma-metrics were assessed.

The context and performance data

This study "was conducted in the Clinical Biochemistry Laboratory at the Government Institute of Medical Sciences, Greater Noida, Uttar Pradesh....The study collected IQC and EQC data from November 2023 to July 2024. QCs were run on two fully automated analyzers. The Selectra Pro M by EliTech Group for routine biochemistry analytes....Daily IQC assessments were conducted at two levels, Level-1 (L1) and Level-2 (L2) for routine biochemistry analytes...Periodic assessment was done usin gEQC materials. All reference materials werer procured from Bio-Rad Laboratories."

"The study was carried in two phases, where first phase involved the retrospective data analyis for a period of 6 months (November 2023-April 2024) based on sigma metrics. After the first phase, QGI [Quality Goal Index] of the analytes performing poorly on the sigma scale was calculated and categorized for imprecision and inaccuracy. Appropriate quality improvement interventions were implemented in the second phase, and data were collected and analyzed prospectively over 3 months (May-July 2024) using sigma metrics."

So we have some good practices here, use of independent control materials, over a longer period of time. The TEa goals (allowable total errors) were taken from CLIA 1992 and RCPA, and later on, they used the CLIA 2024 goals to see how the metrics would change under stricter requirements.

"RCA analysis was done and quality improvement interventions such as improvements in standard operating procedures, reference material reconstitution, pipette calibration, laboratory's environment, and reagent storage were made. Special attention was given to ensuring staff competence and skills, with periodic assessments to monitor improvements in poorly performing analytes."

Overall, performance of the Selectra Pro M was far from great, either before or after the interventions. There were some analytes that clocked in below 1 Sigma. Indeed, in some cases, the Sigma metric went down after post-improvements.

"Frequent equipment breakdowns, delayed preventive maintenance, reagent storage, laboratory environment, changes in reference material lots, and water quality issues may explain the below-average performance of some analytes."

Nevertheless, even with a challenging laboratory environment and a less-than-cutting-edge instrument, improvements were still possible and tangibly felt:

The final improvements mean that in total 104,342 defects per million were eliminated from the operation of the instrument, essentially a 10% reduction of defects. This lab won't literally see 104,000 fewer errors (unless they happened to have a sample volume of one million patients). Their benefits will be experienced as an average of 10% fewer defects over their actual volume. You'd like to see more benefits, but a double-digit gain is nothing to sneeze at.

In terms of other benefits the laboratory could realize, the number of Westgard Rules needed for QC has a greater gain. In the pre-assessment phase, basically all methods needed to use all the Westgard Rules. In the post-improvement phase, the number of rules needed for QC was reduced by 20%. After improvements, all the Westgard Rules aren't needed on all the tests, with some tests only needed a single rule for QC. That benefits the laboratory's operating cadence, and will also reduce the number of false rejections experienced.

We might prefer even more dramatic improvements, possibly enabled by selection of a better instrument. But if the laboratory is not switching boxes, than we seek to wrest what improvements we can out of the box they have.

In conclusion, there are real gains to be made with Sigma metrics, even with imperfect conditions and imperfect instrumentation. This laboratory is but one demonstration of the benefits.