SIX SIGMA ESTIMATES FOR HIGH VOLUME HEMATOLOGY
ANALYZERS - BECKMAN COULTERSIX SIGMA ESTIMATES FOR HIGH VOLUME HEMATOLOGY
ANALYZERS - BECKMAN COULTER |
[Note: This QC application is an extension of the lesson From Method Validation to Six Sigma: Translating Method Performance Claims into Sigma Metrics. This article assumes that you have read that lesson first, and that you are also familiar with the concepts of QC Design, Method Validation, and Six Sigma. If you aren't, follow the links provided.] |  |
A month ago, we provided a Six Sigma analysis of the CAP Today survey data on High volume hematology analyzers. The process for doing this was explained in our lesson on how to convert precision claims into Six Sigma estimates, we thought it would be useful to put that lesson into action, using the public data available in the CAP Today surveys.
That analysis, while valuable, was incomplete. The CAP Today survey only included data on the imprecision. To get a more realistic picture of instrument performance, you also need to look at the available estimates on bias (inaccuracy).
Sadly, few companies were able to provide us with the additional data. So we are especially grateful to Beckman Coulter for providing us with their data on inaccuracy for their four instruments.
[ For the purposes of this application, we are not going to walk through the steps of the calculations (see the previous article links or the recap below to see how these numbers are calculated). We will only present the final results here and discuss them. ]
The CAP Today survey collects data provided by the manufacturers themselves. These companies have given their precision claims. In fact, manufacturers are required to provide precision and accuracy claims when they market a diagnostic device. Nevertheless, it is often difficult to find this data.
Note that in the CAP Today survey, no details of how these precision claims were created are available. We, as readers, must accept them on faith. In the data provided by Beckman Coulter, better details are available. Indeed, you can download the spreadsheet here.
Here are the Precision Claims along with the Sigma metrics:
| Analyte | RBC Erythrocytes |
WBC Leukocytes |
Hb Hemoglobin |
Pt Platelet Count |
||||||||
| Total Allowable Error % | +/- 6% | +/- 15% | +/- 7% | +/- 25% | ||||||||
| Instrument | Precision Claim | Bias Claim | Sigma Estimate | Precision Claim | Bias Claim | Sigma Estimate | Precision Claim | Bias Claim | Sigma Estimate | Precision Claim | Bias Claim | Sigma Estimate |
| Coulter LH700 | 0.80 | 2.00 | 5.00 | 1.70 | 3.50 | 6.76 | 0.80 | 3.00 | 5.00 | 3.30 | 7.00 | 5.45 |
| Gen-S System | 0.80 | 2.00 | 5.00 | 1.70 | 3.00 | 7.06 | 0.80 | 3.00 | 5.00 | 3.30 | 7.00 | 5.45 |
| Coulter LH500 | 2.00 | 2.00 | 2.00 | 2.50 | 3.50 | 4.60 | 1.50 | 3.00 | 2.66 | 5.00 | 7.00 | 3.60 |
| Coulter HMX | 2.00 | 2.00 | 2.00 | 2.50 | 3.00 | 4.80 | 1.50 | 2.00 | 3.33 | 5.00 | 7.00 | 3.60 |
Overall, these data are encouraging. We see that the Sigma metrics for the LH700 and Gen-S System are at 5.0 or higher than Six Sigma - excellent news. Performance is very good and the ideal goal is not far away.
For the Coulter LH500 and HMX, performance for leukocytes and platelet count is good, but for hemoglobin and erythrocytes, the metrics are somewhat concerning. This is in part due to the fact that the quality requirements for erythrocytes and hemoglobin are relatively tight ( 6 and 7 percent, respectively).
What do you do with Sigma metrics? One thing you can do is QC Design and Planning. There are a number of QC Design tools listed below
1. Sigma Metrics Estimates are still estimates.
The real metric that matters is how the method performs in your laboratory. Getting more information is critical to your decision process. Method Validation results, ideally from studies that you run in your lab, will provide you with the best information.
With Sigma metrics calculated from performance claims, you may be able to better recognize poor performance and eliminate those methods from your consideration.
2. All instruments are not created equal.
Looking over the data provided by the CAP Today survey, as well as the data provided by Beckman Coulter, reveals a wide range of performance. It would be tempting to think that all companies provide performance at about the same level, but the data clearly doesn't support that. And it would be similarly tempting to assume that within a company, all their instruments perform with the same level of quality. That myth, too, can now be dispelled. Perhaps the biggest lesson to learn is that you must always evaluate the claims to determine Sigma performance. No brand can guarantee excellence.
3. What would you do?
Undoubtedly, the precision claim is not the only factor that goes into the decision to purchase an instrument. But it is worth wondering, how important is the. If you know that a method will require you to run 4 or more controls and use "Westgard Rules", will that affect your decision? Will you accept poor method performance in favor of speedy test results? Let us know your thoughts.
- Normalized OPSpecs charts are available as a free download from the website.
- The OPSpecs Manual, Expanded Edition, offers a low cost, manual QC Design technique.
- EZ Rules® is a software program that automates the rule selection process for QC Design
- QC Validator® is a software program that gives fine-grained, custom control over automatic QC Selection
