Hook effect

The phenomenon is caused by very high concentrations of a particular analyte or antibody and is most prevalent in one-step (sandwich) immunoassays.

If the antibodies interact with the antigen to form immune complexes, called agglutination, then the test is interpreted as positive.

[5] The effect can also occur because of antigen excess, when both the capture and detection antibodies become saturated by the high analyte concentration.

However, when the serum is diluted, the blocking antibody is as well and its concentration decreases enough for the proper precipitation reaction to occur.

[10] In other words, getting the rabbits' bodies to produce more antibodies against this bacterium had the counterproductive effect of decreasing their immunity to it.

[10] One kind of relevance that he hypothesized for this in vivo blocking antibody concept was as a driver of human susceptibility to certain infectious diseases.

Illustration of hook effect adapted from Schiettecatte et al. [ 1 ]
Illustration of the effects of excess antigen and blocking antibodies on immunoassays.
Simple illustration of the effects of excess antigen and dosage response curve.