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November 19, 2013


Carol Antivo

I would contact Tech Support of the instrument you are having trouble with your QC

It could be an instrument issue.


Most laboratories would just exclude the data point that is out of control during establishing QC, without investigating the reason behind it. Hence they ended up with a very tight SD. During the routine operation, they would inevitably encounter out of control situation, which they would exclude and repeat and repeat.
So I do advice them that; during the evaluation period of an assay, lab should inform manufacturer if do not conform to manufacturer claim. Suppose the CV conform to the manufacturer's claim but did not conform to the Biological Variation Imprecision requirement. Can lab still set the SD based on the manufacturer's claim? (Lets assume the lab had accepted the assay based on the manufacturer's claim and subsequently a new manager wants lab to set SD based on the Ricos Biologic Variation ;desirable imprecision requirement)

Hans van Schaik

When applying your own calculated mean and SD value it is very important to keep in mind that lot changes might cause a shift in the mean value,and enlarge the SD. The impact of this lot change depends on the tolerance the manufacturer applies to the reagentproduction. It might be the cause of an out of control situation, after a long period of stable performance.

Kathleen M. Spiegel PhD MT(ASCP)

Questions I would ask. Were the QC limits calculated on the basis of the same lot number of the QC that is now repeatedly out? Has a change occurred in the QC material itself-(storage, concentration, source.) If the QC material in question were run repeatedly, does the mean differ from the recent historic mean-and not so recent mean ( someone tweaking control levels rather than addressing changes over time?). I am assuming a reserved lot number. if so it is a QC material problem and I do not see that this has been ruled out in the example.

Steve Young

One night (in 1996), I was working alone and my Creatinine was out on one control, -2SD in the same direction. I did the usual, tried to use my backup instrument, reconstituted new QC material, and no change, maintenance on both instruments. Nothing helped. So I pulled the last 30 days QC records (QC every 2 hours back in those days) and recalculated the QC. The mean dropped by 0.1 and the 1sd expanded by 0.04 mg/dl. This was enough to bring my QC to within 1sd. Wrote everything up for my supervisor and reported my work. Took about an hour, but I was confident my results were valid and my instruments were wroking. Two day's later, the supervisor published new creatinine ranges using many of the justifications I used in my report to her.


I have a question about CV. One portion of AAPS advocates use of a CV that uses SD/nominal rather than SD/mean. Since the widely accepted formula and its definition (CV) is SD/mean, would it not be more appropriate to push for an alternate abbreviation so the two could be distinguihed? Also what is the advantage of calculating SD/nominal?

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