Sensitivity Limit
Definition
The minimum amount of blood (or age/dilution of stain) at which the crystal test can still produce identifiable crystals. Below this threshold the test yields no crystals or atypical fragments.
- Applies to
- Teichmann and Takayama crystal tests
- Measures
- Minimum blood amount or maximum stain age/dilution
- Below threshold result
- No crystals or atypical fragments
- Field
- Presumptive and confirmatory blood identification
- Relevance
- Sets the practical floor for usable stain size
Common questions
Why do old or heavily diluted bloodstains fail the crystal tests even when blood is truly present?+
Both tests rely on forming crystalline derivatives of hemoglobin breakdown products, and as a stain ages or is diluted, the concentration and integrity of these compounds drop below the level needed to nucleate recognisable crystal shapes, producing an inconclusive or negative result despite a true bloodstain.
Does a negative result below the sensitivity limit rule out blood?+
No, a negative or atypical crystal result on a very small, old, or diluted stain is inconclusive rather than exculpatory, and examiners should not report it as proof blood is absent; a more sensitive presumptive test or DNA analysis may still succeed on the same stain.
How does the sensitivity limit differ between the Teichmann and Takayama tests?+
The two tests use different reagents and crystal-forming chemistry, so their practical detection floors and the appearance of atypical or degraded crystals can differ somewhat, which is one reason laboratories may run one as confirmation for the other on marginal samples.
Related terms
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