Prozone Effect
Definition
A false-negative serological result caused by antibody excess. When antibody concentration is too high relative to antigen, antibodies saturate individual antigen molecules without cross-linking them, preventing lattice formation and the visible precipitation or agglutination needed to read a positive result.
- Cause
- Antibody excess relative to antigen
- Result type
- False negative
- Mechanism
- Antibodies saturate antigen sites without cross-linking
- Fix
- Dilute the sample and retest
- Sub-field
- Forensic serology, agglutination and precipitation assays
Common questions
How would an analyst notice a prozone effect during testing?+
A sample that behaves inconsistently, such as showing weak or absent agglutination at full strength but a clear positive after dilution, signals that antibody excess may have masked the true result at the original concentration.
Which serological methods are most vulnerable to the prozone effect?+
Direct agglutination and precipitation reactions that depend on visible lattice formation are most affected, since these rely on antibodies bridging multiple antigen particles rather than simply binding one epitope each.
What is the practical laboratory response to a suspected prozone result?+
Standard protocol is to retest at several dilutions, since a true positive will reappear once antibody concentration drops enough to allow lattice formation, while a genuine negative stays negative across dilutions.
Related terms
- 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...
- Anti-Human Haemoglobin Antibody
- A monoclonal antibody raised against epitopes unique to human haemoglobin. Forms the detection and capture antibodies on the lateral-flow strip, conferring specificity...
- Complement
- A group of heat-labile serum proteins (approximately 30 proteins, designated C1 through C9 in the classical pathway) that can be activated by...
- Complement Fixation
- The binding and consumption of complement proteins by an antigen-antibody immune complex. Once fixed, complement is no longer available for the lytic...
- Control Band (C Line)
- A second line that captures excess labelled antibody regardless of whether the analyte is present. Its appearance confirms the assay ran correctly....
- Indicator System
- In the complement fixation test, sheep red blood cells pre-coated with anti-sheep-RBC antibody (sensitised cells). These cells are lysed by free complement...
- Lateral-Flow Immunochromatography
- A test format in which a liquid sample flows laterally along a membrane, encounters labelled detection antibodies, and is captured at specific...
- Postzone Effect
- A false-negative serological result caused by antigen excess. When antigen greatly exceeds antibody, both binding sites on each antibody molecule are occupied...
- Test Band (T Line)
- The line on the lateral-flow card that appears when the anti-haemoglobin antibody captures haemoglobin-laden conjugate. Its presence constitutes a positive result.
Explained in these topics
- Complement Fixation and Mixed Antigen-Antibody Reactions
- RSID-Blood and ABAcard HemaTraceParadoxical inhibition of the test band when haemoglobin concentration is extremely high, as excess antigen saturates all antibody binding sites and prevents t...