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Measurements near an IVD decision boundary may move between result categories with small differences. Overall agreement across the full range may not explain this behaviour. Make the boundary region visible in a way that fits the research question.
Define the assessment
Explain when the decision rule was established and which data informed it. Do not exclude borderline specimens because they worsen results. Separate technical variability, reference uncertainty and clinical context; avoid implying independent validation when the same data selected and assessed the boundary.
Worked example
For example, high- and low-level specimens produce consistent categories, while some near the boundary change category on repetition. The team reports more than overall agreement. It explains representation of the relevant range, the repeat design and the result rule, identifying which findings require technical assessment or clinical interpretation.
Practical checks
- State the number and selection method of specimens around the boundary.
- Retain links between raw measurements, categories and repeat results.
- Make separation of boundary-development and assessment data visible.
Decision and limitations
The report should show behaviour across the relevant range. Borderline variability does not automatically make a test worthless, but requires interpretation of use rules and uncertainty. Authorised reviewers assess implications for instructions or claims; the study team should not silently change clinical decision rules.
Frequently asked questions
- Can borderline specimens be excluded?
- Avoid arbitrary result-driven exclusions. Define and justify eligibility and analysis rules.
- Is high overall agreement sufficient?
- It does not alone explain behaviour near the boundary; that range may need separate assessment for the intended decision.