Cross-Reactivity Matrix
Definition
A table documenting the assay's optical density response to blood from multiple non-target species, expressed as a percentage of the human blood response. An essential component of any forensic validation report for an immunoassay.
- Content
- Assay response to blood from multiple non-target species
- Unit reported
- Percentage of the human blood optical density response
- Report requirement
- Standard component of an immunoassay validation report
- Applies to
- Anti-human haemoglobin ELISA and similar immunoassays
Common questions
Why test the assay against animal blood at all if it targets human haemoglobin?+
Antibody-based assays are rarely perfectly specific. Close relatives such as other primate blood can produce a partial signal, so the matrix quantifies how much cross-reaction to expect and lets an examiner judge whether a low positive result could be a non-human source.
How should a low but positive cross-reactivity value be interpreted in casework?+
It sets a threshold below which a result is treated as inconclusive for species origin rather than a confirmed human-blood call, and it is one reason presumptive and confirmatory human-specific tests are kept separate in the workflow.
Related terms
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- Optical Density (OD)
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- Sandwich ELISA
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- Standard Curve
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