Posted by Sten Westgard, MS
A recent question came in from outside the US, regarding the choice of controls and EQA/PT provider. In such a case, there are often economies gained by choosing the same vendor for both control materials and EQA/PT materials. But the theory of quality control and assurance dictates that you should have independent checks on your processes. Indeed, in some countries, there are regulations which prevent control manufacturers from selling proficiency testing materials for precisely that reason.
This is a difficult issue, one that epitomizes the struggle between efficiency (cost) and safety (quality).
More after the fold...
Here is the principle behind the choice of separate vendors for the instrument and the controls, as well the choice of separate vendors for controls and EQA/PT. If you go with just one control/EQA provider, that choice exposes you to the chance that a systematic error will go undetected by both QC and EQA. Since the manufacturer will probably be recalibrating, synchronizing, and adjusting their instrument and control materials together, for example, that will make them act the same way.
In contrast, the benefit of EQA/PT with a third-party manufacturer is that it will be an independent check on the instrument performance. Since their controls or EQA materials will be different, they will be sensitive to errors that the manufacturer's system is not.
Just to restate the idea of PT/EQA, indeed the idea of third-party QC materials: the lab needs an independent check on the performance of the instrument. If you lose that independent check, it doesn't automatically mean an error will occur. But it does make you more vulnerable to a possible error. If your controls, EQA/PT, and instrument are all unrelated, you have maximized your ability to detect errors that might occur.
So that's the theory. But when I discussed this with a colleague in the controls business, one who deals with customer problems daily, the reality of the situation showed that a bit of nuance may be helpful.
For one, the customer can inquire and determine if the EQA/PT specimens and the controls are in fact the same material. If they are different, particularly if they are of different matrices, that increases the chance that a problem not detected by one material may still be detected by the other. Furthermore, even if they are similar materials, that vulnerability could still be lessened if different lots are being used for the controls than for EQA/PT. Given the different way that QC materials and PT materials are ordered and distributed, it would be highly unlikely that the same lot of material would be used at the same time.
So, with a bit of due diligence, it may be possible to choose the same vendor for both PT and controls. Just keep in mind that you need to think of a way to run a check that could catch the errors that both PT and controls might miss.
Comments