TNI Logo The NELAC Institute

Standard Interpretation

Standard: 2016
Section: V1M5, Section


My question is regarding the Test Variability/Reproducibility section in the new 2016 standard. The verbiage essentially states to perform for methods that specify counts (i.e., cfu/100 mL or MPN/100mL)..." or other methods which specify a quantitative result." My question is, was the intent to hold labs accountable for performing this for IDEXX Quanti-tray as well? It is an MPN method; however, I did not feel the intent was to perform for this method but rather other MPN methods (e.g., multiple tube fermentation). Furthermore, if a laboratory is not obtaining any positive samples over the course of a month using this method, would they still be required to perform one? Standard methods instructs to perform this for plate counting methods, so I wanted to make sure the intent as to what methods to hold labs accountable for.


The standard is clear on the inclusion MPN methods and this does not exclude Quanti-tray. Furthermore, the STD states 'duplicate counts shall be performed monthly'. It would be up to the lab to determine how they obtain the positive sample with which to perform the counts.