Characteristics to Consider when Selecting a Positive Control Material for an In Vitro Assay

The use of in vitro assays to inform decision-making requires robust and reproducible results across studies, laboratories, and time. Experiments using positive control materials are integral to demonstrating the extent to which a measurement system is performing as expected. A paper by CPSC, NIEHS, and NIST scientists and collaborators (Petersen et al. 2021) reviewed 10 characteristics that should be considered when selecting a positive control material for an in vitro assay. These include: (1) the biological mechanism of action, (2) ease of preparation, (3) chemical purity, (4) verifiable physical properties, (5) stability, (6) ability to generate responses spanning the dynamic range of the assay, (7) technical or biological interference, (8) commercial availability, (9) user toxicity, and (10) disposability. The paper presented examples and a case study of the monocyte activation test to demonstrate the application of these characteristics for identification and selection of potential positive control materials. Because specific positive control materials are often written into testing standards for in vitro assays, selection of the positive control material based on these characteristics can aid in ensuring the long-term relevance and usability of these standards.