The borderline range of toxicological methods: quantification and implications for evaluating precision
Open accessAbstract
Test methods to assess the skin sensitization potential of a substance usually use threshold criteria to dichotomize continuous experimental read-outs into yes/no conclusions. The threshold criteria are prescribed in the respective OECD test guidelines and the conclusion is used for regulatory hazard assessment, i.e., classification and labelling of the substance. We can identify a borderline range (BR) around the classification threshold within which test results are inconclusive due to a test method's biological and technical variability. We quantified BRs in the prediction models of the non-animal test methods DPRA, LuSens and h-CLAT, and of the animal test LLNA, respectively. Depending on the size of the BR, we found that between 6% and 28% of the substances in the sets tested with these methods were considered borderline. When the results of individual non-animal test methods were combined into integrated testing strategies (ITS), borderline test results of individual tests also affected the overall assessment of the skin sensitization potential of the testing strategy. This was analyzed for the 2-out-of-3 ITS: Four out of 40 substances (10%) were considered borderline. Based on our findings we propose expanding the standard binary classification of substances into "positive"/"negative" or "hazardous"/"non-hazardous" by adding a "borderline" or "inconclusive" alert for cases where test results fall within the borderline range.
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Assay variability near decision points may be large enough to affect classification, particularly where the threshold is close to the steep part of a concentration-response curve.
“Ring-trial and validation data indicate that assay variability near decision points may be large enough to affect classification, particularly where the threshold is close to the steep part of a concentration-response curve (Kolle et al., 2021; Gabbert et al., 2022; Leontaridou, 2017).”
From Cytotoxicity across OECD methods is not a single endpoint: context-dependent roles, variability and implications for decision-making (2026) · cites this paper as Leontaridou, 2017
The Abstract says biological and technical variability can make results near classification thresholds inconclusive and can affect the overall assessment. It does not link that effect specifically to thresholds on the steep part of a concentration-response curve or identify ring-trial data as its basis. (LLM, conf=0.85)
Experimental — accuracy not yet measuredThe concept of borderline ranges is well established for several defined approaches and in vitro skin sensitization methods.
“The concept is well established for several defined approaches and in vitro skin sensitization methods (Kolle et al., 2021; Gabbert et al., 2022; Leontaridou, 2017; OECD, 2025e).”
From Cytotoxicity across OECD methods is not a single endpoint: context-dependent roles, variability and implications for decision-making (2026) · cites this paper as Leontaridou, 2017
The Abstract reports quantified borderline ranges for three non-animal skin-sensitization methods and examines their effect on one integrated testing strategy. It does not establish that borderline ranges were already well established across several defined approaches; instead, it proposes adding a borderline alert to standard classifications. (LLM, conf=0.85)
Experimental — accuracy not yet measured
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Research works printed but not linked: 10
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Cited by
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Non-animal methods to predict skin sensitization (I): the Cosmetics Europe database
Hoffmann, S., Kleinstreuer, N., Alépée, N., Allen, D., Api, A. M., Ashikaga, T., Clouet, E., Cluzel, M., Desprez, B., Gellatly, N., et al. (2018) · Critical Reviews in Toxicology · doi:10.1080/10408444.2018.1429385 · Cited by 188 · see citing works
Blum, J., Masjosthusmann, S., Bartmann, K., Bendt, F., Dolde, X., Dönmez, A., Förster, N., Holzer, A.-K., Hübenthal, U., Keßel, H. E., et al. (2023) · Chemosphere · doi:10.1016/j.chemosphere.2022.137035 · Cited by 105 · see citing works
Thoma, T., Löhr, L., Demuth, P., Hambruch, N., Oesch, F., & Landsiedel, R. (2026) · NAM Journal · doi:10.1016/j.namjnl.2026.100126
- Authors
- Leontaridou, M.
- Affiliations
- BASF (Germany) (DE)
- Corresponding author
- Leontaridou, Maria
- Venue
- ALTEX
- Publisher
- ALTEX Edition
- Published
- 2017
- Volume
- 34
- Issue
- 4
- Pages
- 525-538
- ISSN
- 0946-7785 (ISSN-L)
- 1868-596X
- OpenAlex
- W2765277177
- Cited by
- 46
- References
- 0
- Citations by year
- 2026: 2 · 2025: 2 · 2024: 1 · 2023: 1 · 2022: 7 · 2021: 4 · 2020: 7 · 2019: 5 · 2018: 11 · 2017: 6
- FWCI
- 9.01
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- cc-by
- Locations
- ALTEX (publishedVersion, cc-by)
- PubMed (publishedVersion)
- Socio-Environmental Systems Modeling (acceptedVersion, cc-by)
- Zenodo (CERN European Organization for Nuclear Research) (submittedVersion, cc-by)
- Data Archiving and Networked Services (DANS) (submittedVersion, cc-by)
- Topics
- Health Sciences › Medicine › Dermatology › Contact Dermatitis and Allergies
- Health Sciences › Veterinary › Small Animals › Animal testing and alternatives
- Life Sciences › Immunology and Microbiology › Immunology › Immunotoxicology and immune responses
- Keywords
- skin sensitization, classification threshold, DprA, integrated testing strategies, test precision, hazard assessment, indeterminate results, binary classification
- MeSH terms
- Animal Testing Alternatives, Humans, Reference Values, Toxicity Tests, Skin Irritancy Tests
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