Overview - ISO 11781:2025 (Qualitative real‑time PCR single‑lab validation)
ISO 11781:2025 provides requirements and guidance for single‑laboratory validation of qualitative (binary) real‑time PCR methods used to detect specific DNA sequences in foods. The standard targets molecular biomarker analysis for applications such as GMO detection, species determination (including allergenic species), and food authentication. It specifies minimum performance criteria (e.g., LOD95, specificity, robustness) and describes statistical approaches for interpreting low‑copy PCR data. Note: the standard does not cover microbiological real‑time PCR nor DNA extraction procedures (see ISO 21571 for extraction).
Key topics and technical requirements
- Limit of Detection (LOD95): LOD is expressed as the mean number of DNA copies giving a 95% probability of detection (POD). Determination requires a dilution series with background (non‑target) DNA; a minimum of six concentration levels with 12 replicates per level is required. The LOD95 should not exceed 20 copies of the target sequence. For method verification, reduced replicate numbers (e.g., 10) may be acceptable.
- Probability of Detection (POD): Quantifies the chance of a positive result at a given copy number; POD curves and 95% confidence intervals are derived from validation data.
- Statistical model: A generalized linear mixed model (GLMM) with a complementary log‑log link (including a Poisson component for low copy numbers) is recommended to estimate LOD95 and POD. The standard references tools such as an R package (POD) and web services for calculations.
- Copy number estimation: Guidance is given for calculating copies per reaction from DNA concentration or using digital PCR (e.g., droplet dPCR) as an alternative for accurate copy quantification.
- Specificity & robustness: Requires both in‑silico (bioinformatic) and practical specificity testing; robustness testing evaluates deliberate small changes to method parameters.
- Documentation: A validation report must summarize protocol, data, statistical analysis, and conclusions. Annexes (A–D) give methods for copy estimation, LOD determination, GLMM details and robustness testing.
Practical applications and users
- Laboratories validating new qualitative real‑time PCR assays for food testing (GMO labs, food authenticity labs, allergen/speciation testing)
- Assay developers and manufacturers preparing in‑house validation data
- Accreditation bodies and quality managers assessing method fitness for purpose
- Researchers planning single‑laboratory validation or considering progression to collaborative (interlaboratory) studies
Related standards (applicable)
Keywords: ISO 11781:2025, single‑laboratory validation, qualitative real‑time PCR, LOD95, POD, PCR efficiency, specificity, robustness, food testing, GMO detection, digital PCR, GLMM.