Inhibitor
Definition
A substance in the sample matrix that interferes with one or more steps in an immunoassay, reducing signal generation from a genuinely positive sample. Common forensic inhibitors include haem, melanin, indigo dye, and bile salts.
- Field
- Serological and immunoassay testing
- Effect
- Reduces signal from a truly positive sample
- Common sources
- Haem, melanin, indigo dye, bile salts
- Risk
- False negative result
Common questions
How does an examiner tell an inhibited result apart from a genuine negative?+
Running an internal positive control or a dilution series on the same sample can reveal inhibition, since a diluted extract sometimes recovers signal that a concentrated, inhibitor-laden extract suppressed entirely.
Why does denim or heavily dyed fabric commonly cause inhibition?+
Indigo dye and other textile dyes can interfere directly with the antibody-antigen reaction or with the enzyme step used to generate a visible signal, which is a known source of false negatives in casework involving dark clothing.
Related terms
- 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...
- 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 that indicates the presence of a target analyte when it is absent. In forensic serology this may mean incorrectly...
- 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...