Interassay

Interassay is a term used in analytical chemistry and bioassays to describe the variation in measurements obtained when an assay is performed in separate runs, on different days, by different operators, or with different instrument setups. It is a measure of between-run or between-assay precision and is contrasted with intra-assay variation, which arises within a single run.

To quantify interassay performance, multiple independent runs are conducted on the same samples and the results are analyzed. Common metrics include the mean, standard deviation, and the coefficient of variation (CV). A lower interassay CV indicates greater reproducibility across runs. The acceptable level of interassay variability depends on the assay type and purpose; many clinical or research immunoassays aim for CVs in the low to mid-single digits or up to the mid-teens.

Factors contributing to interassay variability include reagent lot differences, calibration and instrument performance, operator technique, ambient conditions, sample stability and handling, and the use of different plates or consumables. Strategies to reduce interassay variability include using the same lot of critical reagents when possible, rigorous calibration and quality control procedures, standardized operating protocols, running appropriate controls and calibrators in every assay, proper sample handling and storage, and careful data normalization.

In regulatory and validation contexts, interassay precision is part of an overall assessment of assay reliability and can be reported alongside intra-assay and inter-laboratory precision. Related concepts include inter-laboratory variation and interchangeability of assay results.