False Negative
Definition
A negative result from a preparation in which ante-mortem drowning actually did occur. Causes include low diatom density in the drowning water, brief submersion, technical losses, and seasonal diatom minima. False negatives demonstrate that a negative result cannot exclude drowning.
- Definition context
- Diatom test for drowning, serological testing
- Causes
- Low diatom density, brief submersion, technical losses, seasonal minima
- Key implication
- A negative result cannot exclude drowning
- Related term
- False positive rate
Common questions
Why can't a pathologist rule out drowning just because the diatom test came back negative?+
Diatom concentration in water varies by season and location, and technical losses during sample preparation can strip diatoms that were present, so a negative result only means diatoms were not detected in that sample, not that drowning did not occur.
How do investigators compensate for the false negative risk in diatom testing?+
They interpret the test alongside scene circumstances, autopsy findings, and other drowning indicators rather than relying on diatom results alone, since the test is better at supporting a positive finding than at excluding drowning.
Related terms
- False Positive
- A test result that indicates the presence of a target analyte when it is absent. In forensic serology this may mean incorrectly...
- 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...
- Confirmatory Hierarchy
- The structured sequence of tests applied to biological evidence, in which a presumptive (screening) test with high sensitivity is followed by a...
- Cross-Reactivity
- The capacity of an antibody raised against one analyte to bind structurally related compounds. In RIA, cross-reactivity is the main driver of...
- 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...
- Hook Effect
- An artefact in sandwich immunoassays (ELISA, lateral-flow) where excess antigen saturates both capture and detection antibodies independently, preventing sandwich formation and producing...
- Inhibitor
- A substance in the sample matrix that interferes with one or more steps in an immunoassay, reducing signal generation from a genuinely...
- Positivity Threshold
- The minimum number of frustules per gram of tissue or per slide that a laboratory uses to declare a result positive. No...
- 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 these topics
- Limitations and Controversies of the Diatom Test
- Sources of Error and False Results in Serological TestingA test result that indicates absence of a target analyte when it is present. In forensic serology this may mean failing to identify a body fluid or blood group...