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Evaluation in one specimen type does not automatically establish the same IVD performance in another. Collection method, matrix and processing conditions may differ. An evidence bridge requires more than a statement that two sets of results look similar.
Define the assessment
Define which specimen types belong to each intended-use claim. Even paired specimens from one person can differ in collection timing and handling. Show whether the comparison examines a technical relationship or a link to clinical performance, preventing conclusions beyond its scope.
Worked example
For example, plasma use is proposed for an assay evaluated in serum. The team examines samples near the clinical decision boundary, discordant outcomes and collection conditions rather than only comparing means. It discloses uncertainty for the new matrix and avoids presenting expanded intended use before authorised assessment is complete.
Practical checks
- Define specimen type, collection device and processing conditions in the comparison plan.
- Verify identity and timing links between paired specimens.
- Examine decision-boundary differences and unrepresented measurement ranges.
Decision and limitations
Acceptance should explain which properties the bridge supports and which questions remain. Similar means do not establish identical decisions for every individual. Connect technical and clinical findings to the relevant claim; a specimen-type change is more than a logistical convenience.
Frequently asked questions
- Are paired specimens from one person sufficient?
- Identity matching matters, but timing, handling and methodological suitability also need assessment.
- Do similar means establish equivalence?
- Not alone. Use a comparison appropriate to individual differences and the intended decision.