Postzone Effect
Definition
A false-negative serological result caused by antigen excess. When antigen greatly exceeds antibody, both binding sites on each antibody molecule are occupied by separate antigen molecules, again preventing cross-linking and lattice formation. Also called the antigen excess effect.
- Cause
- Antigen in large excess over antibody
- Result
- False-negative serological reaction
- Mechanism
- Antibody binding sites saturated by separate antigens, no cross-linking
- Also called
- Antigen excess effect
Common questions
How is a postzone false negative usually caught in practice?+
Serial dilution of the sample is standard practice precisely to detect this: diluting a strongly antigen-excess sample moves the antigen-antibody ratio back toward the zone where lattice formation and visible reaction occur, converting an apparent negative into a positive.
How does postzone differ from prozone, the other antigen-antibody excess effect?+
Prozone is caused by antibody excess and is the more commonly discussed of the two in serology, while postzone is caused by antigen excess; both produce the same practical problem of a false negative through failed cross-linking, just from opposite directions of imbalance.
Related terms
- 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...
- 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...
- 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...
- Prozone Effect
- A false-negative serological result caused by antibody excess. When antibody concentration is too high relative to antigen, antibodies saturate individual antigen molecules...