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ICCVAM Biennial Report 2020-2021

Biennial Progress Report 2020-2021 Interagency Coordinating Committee on the Validation of Alternative Methods

Variability Analysis of In Vivo Skin Irritation Data to Use in Establishing Confidence for Alternative Methods

A limiting factor in identifying a complete in vitro replacement for the standard in vivo skin irritation test could be the variability inherent to the subjective scoring of endpoints in the in vivo test. This is particularly relevant for mild and moderate irritants, where interindividual differences in scoring are most likely to occur. To characterize the reproducibility of the in vivo assay, NICEATM assessed variability in study results from substances tested multiple times (Rooney et al. 2021). A set of 2,624 test records was compiled and curated, representing 990 unique mono-constituent substances, each tested at least twice. Conditional probabilities were used to evaluate the reproducibility of the in vivo method in identification of EPA or GHS hazard categories. Chemicals classified as moderate irritants at least once were classified as mild irritants or non-irritants at least 40% of the time when tested repeatedly. Variability was greatest between mild and moderate irritants, for which each type of substance had less than a 50% likelihood of its classification being replicated. This analysis indicates that variability of the rabbit skin irritation test should be considered when evaluating the performance of non-animal alternative methods as potential replacements. The analysis was used as a case study in a review (Alves et al. 2021) highlighting the importance of data curation in developing data sets used as inputs for artificial intelligence models.