Positivity threshold
Definition
The minimum number of frustules per gram of tissue or per slide that a laboratory uses to declare a result positive. No universal standard exists; threshold proposals in the literature range widely, and different thresholds applied to the same case can produce opposite conclusions.
Related terms
- Background contamination
- Diatom frustules introduced into a sample from sources other than the victim's own body: tap water, laboratory air, unclean glassware, reagents, and...
- Diatom density
- The number of frustules per unit volume of water in the drowning environment. Low-density environments (pools, tap water, diatom-poor rivers) cannot deliver...
- False negative
- A negative result from a preparation in which ante-mortem drowning actually did occur. Causes include low diatom density in the drowning water,...
- False positive
- A test result indicating diatoms consistent with ante-mortem aspiration in an organ sample when the diatoms actually arrived by contamination, post-mortem diffusion,...
- Standardisation
- The production of a validated, peer-reviewed protocol that specifies every variable in the test: acid type and concentration, digestion time and temperature,...
Explained in
- Limitations and Controversies of the Diatom TestThe minimum number of frustules per gram of tissue or per slide that a laboratory uses to declare a result positive. No universal standard exists; threshold pr...