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Obtaining sufficient positive specimens can be difficult for rare conditions. Additional archived or selected-site specimens may answer some questions but change the sample structure. Do not present enriched data as a natural presentation stream.
Define the assessment
Record which specimens came from consecutive or defined clinical flows and which were selected later. Target levels, clinical stages and handling may differ. The analytical approach should justify when these sources can be combined for particular assessments.
Worked example
For example, routine collection yields few positives, so obvious positives are added from a bank. The team does not assume that a larger count resolves all representation concerns. It examines source, specimen characteristics and comparator methods, reports the banked group separately and avoids inferring real presentation frequency from the enriched distribution.
Practical checks
- Keep specimen source and selection pathway traceable for every record.
- Compare clinical characteristics of added positives with positives from the principal flow.
- Explain the questions answered by combined and separate assessments.
Decision and limitations
The report should show the contribution and limits of added specimens. More positives do not always mean broader clinical representation. Support claims of negligible source effects with evidence; consider separate findings or further assessment. Avoid unconditional performance claims for wholly unrepresented conditions.
Frequently asked questions
- Are added positive specimens unusable?
- They may be useful if selection and source differences remain explicit in assessment and reporting.
- Does an enriched sample show real-world frequency?
- Its selection structure prevents a direct assumption; assess which measures it supports.