Hook Effect
Definition
An artefact in sandwich immunoassays (ELISA, lateral-flow) where excess antigen saturates both capture and detection antibodies independently, preventing sandwich formation and producing a falsely low or negative signal from a strongly positive sample.
- Assay type affected
- Sandwich immunoassays, ELISA, lateral-flow
- Cause
- Antigen excess saturating both antibodies separately
- Result
- Falsely low or negative signal
- True status
- Sample is actually strongly positive
Common questions
How does the hook effect differ from a genuine true-negative result?+
In a true negative, neither antibody binds antigen at all, whereas in the hook effect antigen is abundant but binds capture and detection antibodies independently without linking them, so no sandwich complex forms even though antigen is present in excess.
How is a suspected hook effect confirmed or ruled out in practice?+
The sample is diluted and retested. If diluting a supposedly negative sample produces a positive signal, the original result was a hook effect artefact rather than a true negative, since dilution reduces antigen below the saturating concentration.
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...
- Inhibitor
- A substance in the sample matrix that interferes with one or more steps in an immunoassay, reducing signal generation from a genuinely...