Posted by Sten Westgard, MS
In the December 2011 issue of Point of Care journal, an interesting study was published:
Preanalytical Errors in Point-of-Care Testing: Auditing Error of Patient Identification in the Use of Blood Gas Analyzers, Natalie A Smith, David G Housley, Danielle B. Freedman, Point of Care, Volume 10: Number 4, December 2011.
The study looked at patient identification errors on a blood gas analyzer in various departments in a hospital. Bearing in mind that this is just one type of pre-analytical error, what do you think the rate was? Given around 100,000 tests, what would you guess as the number of defects?
"A total of 1961 errors were identified out of 104,979, giving an overall error rate of 1.9%."
Let's put that into Sigma-metric terms, using the short-term Sigma table: a 1.9% error rate is equivalent to 3.6 Sigma (rounding up). Or, about 17,864 defects per million opportunities.
If the goal of POC testing is to have "lab equivalent" quality, and the generally accepted minimum bar for performance is 3 Sigma, there isn't a lot of room left for other errors for this testing. If we include other possible sources of pre-analytical, analytical, and post-analytical error, we may indeed find that the POC testing is below 3 sigma, which would be considered unacceptable performance in other industries.
Another striking issue is that this error rate (again, for a single type of pre-analytical error) is far higher than some other studies of POC error rates. In the Clin Chem study on POC error rates, the entire error rate (preanalytical, analytical, and postanlytical) for the worst method was just 0.65%, or a 4 Sigma program. This was for the HbA1c methods. Other POC methods had Sigmas of 4.5, 5, 5.6 and even higher.
Three quick points to make:
- Errors do occur at the POC, and they may occur at high rates.
- It looks like there's considerable variability in POC error rates. Some methods, some labs have high error rates, others have low rates.
- If we reduce our QC frequency, how are we going to catch these errors?
As the study itself concludes:
"In summary, our study suggests that quality error rates associated with POCT may be considerably higher than those associated with central laboratory testing. This is important information when assessing the potential risks and benefits of introducing POCT. If the potential risk to patient care is increased, then POCT can be justified only when the potential benefits arising from the rapid availability of a test result are high"
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