Overview
ISO/TS 27878:2023 establishes statistical techniques to determine the reproducibility of the level of detection (LOD) for binary (yes/no) test methods in both collaborative and in‑house validation studies. It covers binary methods for continuous measurands (e.g., chemical concentrations) and discrete measurands (e.g., colony forming units or RNA copies). The technical specification links LOD estimation to probability of detection (POD) models and follows precision concepts from ISO 5725. Importantly, the document addresses not only LOD reproducibility but also the standard error and uncertainty of those estimates.
Key topics and requirements
- Scope of methods: Binary qualitative tests for continuous and discrete measurands.
- LOD definition: Concentration level at which POD reaches a specified value (e.g., 50% or 95%).
- Statistical models: Separate parametric models for continuous and discrete measurands, converting binary outcomes into quantitative LOD estimates.
- Precision and reproducibility: Reproducibility precision estimated according to ISO 5725 (all parts). Emphasis on estimating the uncertainty (standard error) associated with precision estimates.
- Study designs:
- Conventional approach - tests performed under repeatability within labs; variability arises between labs. Recommended minimum designs include at least 8 participants, 5 concentration levels, and 12 replicates per level for more reliable LOD/POD curves (minimum acceptable: 8 participants, 4 levels, 8 replicates).
- Factorial approach - deliberate variation of factors (analyst, instrument, reagent lot, temperature, etc.) to identify specific sources of variability and increase efficiency.
- Reliability checks: Guidance on evaluating the reliability of precision and LOD estimates and on selecting concentration ranges where POD spans expected response (typically 20–80% across levels).
- Software: Reference to software tools for implementing the statistical procedures.
Applications
- Validation of diagnostic assays, microbiological methods, PCR and molecular tests, and chemical qualitative screens where a binary outcome is reported but an LOD characterization is required.
- Informing method acceptance criteria, routine lab quality control, regulatory submissions, and interlaboratory studies by quantifying how LOD varies across laboratories and conditions.
- Designing efficient validation studies (conventional vs factorial) to estimate LOD reproducibility and uncertainty.
Who should use this standard
- Laboratory validation scientists, method developers, quality managers, regulatory assessors, and statisticians involved in method validation and interlaboratory studies.
- Organizations performing collaborative trials or in‑house validation of qualitative/binary assays that require robust LOD and POD estimation.
Related standards
- ISO 5725 (accuracy, trueness and precision of measurement methods)
- ISO 3534-1 (statistics - vocabulary and symbols)
- ISO 16140 series and ISO/TS 16393 (validation protocols for microbiological and qualitative methods)
- AOAC guidelines (relevant validation approaches)
Keywords: ISO/TS 27878:2023, level of detection, LOD reproducibility, binary methods, probability of detection (POD), collaborative validation, in‑house validation, ISO 5725, factorial design, experimental design, validation statistics.