Efficient estimation of the limit of detection and the relative limit of detection along with their reproducibility in the validation of qualitative microbiological methods by means of generalized linear mixed models

The reproducibility of measurement results is a core performance characteristic for quantitative methods. However, in the validation of qualitative methods it is not clear how to characterize a method’s reproducibility. One approach for determining a qualitative method’s reproducibility is presented for microbiological methods, where the distribution of colony forming units (CFU) follows a Poisson distribution. The method’s reproducibility is defined in terms of the variability of the limit of detection (LOD) values. For a better estimation of reproducibility precision, our proposed approach is using an orthogonal factorial plan. Since an exact determination of absolute contamination levels is often not possible, following the ISO 16140-2:2016 [Microbiology of food and animal feed—method validation—part 2: protocol for the validation of alternative (proprietary) methods against a reference method, 2016], an approach is proposed which is based on the ratio of the LOD values of a reference and an alternative method. This approach is illustrated on the basis of an example.