Six Sigma is a method of process improvement which focuses on minimizing variability in process outputs. The Six Sigma model was developed by Motorola in 1986, and Motorola have reportedly saved over $17 Billion due to its successful implementation.

The model looks at the number of standard deviations (SD) or ‘sigmas’ that fit within the quality specifications of the process. In the laboratory, the quality specifications relate to the Total Allowable Error (TEa).  The higher the number of standard deviations that fit between these limits, the higher the sigma score and the more robust the process or method is. As sources of error or variation are removed from a process, the SD becomes smaller and therefore the number of deviations that can fit between the allowable limits is greater; ultimately resulting in a higher sigma score.

A process with a sigma score of six is considered to be a high quality process, making six the target for many industries including the clinical laboratory.

In order to achieve Six Sigma, a process must not produce more than 3.4 defects per million opportunities. In a Laboratory context, this would equate to 3.4 failed QC results per million QC runs.

Sigma is calculated using the following equation:

Sigma = (TEa – %Bias) / %CV

TEa – Total Allowable Error

%Bias – Deviation from the target or peer group mean

%CV – Imprecision of the data

Why is Six Sigma useful in the laboratory?

Six Sigma can be used to help answer one of the most commonly asked questions in laboratory quality control. How often should I run QC?

The Six Sigma model allows laboratories to evaluate the effectiveness of their current QC processes. Its most common use is to help implement a risk-based approach to QC, where an optimum QC frequency and multi-rule procedure can be based on the sigma score of the test in question. The performance of tests or methods with a high sigma score of six or more may be evaluated with one QC run (of each level) and a single 1:3s warning rule. On the other hand, tests or methods with a lower sigma score should be evaluated more frequently with multiple levels of QC and a multi-rule strategy designed to increase identification of errors and reduce false rejections.

The below table shows how multi-rules and QC frequency can be applied according to Sigma Metrics:

Sigma Score	QC Frequency	Number of QC Samples	QC Rules
6 or more	Once per day	Each level of QC	1:3s
5	Once per day	Each level of QC	Multi-rule strategy
4	At least twice per day	Each level of QC	Multi-rule strategy
< 4	At least four times per day	Each level of QC	Multi-rule strategy

 

It is important to note that this is just an example and it may be necessary to run QC samples more often than three times per day.  Some high throughput laboratories prefer to run QC samples before and after a set number of patient samples, while others opt to run QC samples after a set period of time.  Whatever frequency you choose it is vital that the frequency is appropriate for the test in use.  Download our guide ‘How often is right for QC’ to find out more.

What can Randox offer?

Randox’s Acusera 24.7 Live Online is a peer group reporting software application designed to complement the Acusera QC range. The intuitive and user-friendly software boasts some of the most advanced features on the market, and Version 1.6 provides automatic calculation of sigma scores for individual assays, giving the user an at-a-glance overview of assay performance.

Peer group reporting software is an integral part of any modern laboratory seeking to streamline their QC processes and reduce costs. With Acusera 24.7 Live Online, there has never been a better time to implement, save and succeed.

Contact us today to find out how Randox can help your laboratory achieve its goals.