Posted by Sten Westgard, MS
According to a recent CAP Q-Probe, approximately how many glucose tests are being bracketed by QC events?
- 5,000 tests between QC runs
- 500 tests between QC runs
- 50 tests between QC runs
- 5 tests between QC runs
The answer, after the jump
The answer, by my math, is approximately 543 glucose tests are run between each QC event.
This is drawing from median and average data collected in a CAP Q-Probe survey, as detailed in the paper: Documentation of Quality Control and Operating Training at Point-of-Care Testing, Dyhdalo KS, Howanitz PJ, Wilkinson DS, Souers RJ, Jones BA, Arch Pathol Lab Med, Vol 138,1444-1448
Note first that I am not so interested in finding out how much of the POC operations and operators are documented and documenting. I am more interested in the test volumes and the error rates. The study states the median laboratory (out of 106 participating institutions) performed 105,948 glucose tests in a year. The study then states that each institution had an average of 195 QC events. So if we divide, 105,948 by 195, we get just over 543.
Next, we note that the error rate was approximately 3% (About 3.4 Sigma on the short-term scale). But now let's think if there were approximately 5.85 QC outliers in the average institution, that means (round up to 6) about 3,258 POC glucose tests that were possibly impacted by the QC errors.
Of course, this is when operating under a probable 20% allowable error goal. If the allowable error goal for glucose meters was tightened, as has been recommended for several years, to something closer to 15% or 10%, that would undoubtedly make the error rate increase.
No wonder, again, that glucose meters are seen as unreliable. They're very close to below 3 Sigma in performance, which would be unacceptable in many fields outside of healthcare.