Implementing PBMS improvements to USEPA's Cryptosporidium and Giardia methods

The US Environmental Protection Agency (USEPA) has developed a new approach for modifying analytical methods—the performance‐based measurement system (PBMS). Methods 1622 and 1623 are the first microbiological methods from USEPA to be based on PBMS. This approach to method validation and implementation allows the methods to be modified to improve performance, increase laboratory efficiency, or reduce costs, provided that the methods' quality control acceptance criteria are met. Although the PBMS approach to method flexibility is straightforward in principle, laboratories and manufacturers need to understand the requirements and process for USEPA evaluation and approval of modified methods before embarking on studies to demonstrate acceptable performance of a modified version of a method. This article describes the process for conducting modified method acceptability studies for USEPA methods 1622 and 1623 and gives examples of both successful and unsuccessful outcomes.