Evaluating Microbiological Method Equivalence – A Decision Guide

Using an appropriate method is a key step in generating reliable results; and, when those results are to be used to make safety-critical decisions, method selection becomes even more important. For microbiological testing, there are national and international standard methods and various other widely accepted methods. Performance of such methods has usually been validated through some kind of collaborative process or independent review. An independent review may have resulted in some kind of certification. Method validation, with or without independent certification, demonstrates that a method has performance equivalent to an established reference method. Many circumstances can arise that cause a laboratory to change methods. In such an event, how is a laboratory to determine that two methods are equivalent to one another if neither of them is a reference method? In this paper we outline a thought process to guide this decision. The process involves comparing existing validation and/or certification data to determine whether two or more methods have been compared against the same reference method for the matrices of interest using a rigorous experimental and statistical approach. If they have, the methods may be considered equivalent, and a laboratory simply needs to verify its ability to perform them. If they have not, then a formal validation may be needed.