Hook effect

Hook effect or prozone effect is a type of interference which plagues certain immunoassays and nephelometric assays, leading to falsely low results of tested substance in the sample. This effect becomes significant when the substance being tested is present in too high concentrations.

Overview

The hook effect or the prozone effect is an immunology term which refers to the observation that the effectiveness of antibodies to form visible aggregates with antigens decreases with increasing antigen concentration or antibody concentration.

Mechanism

The hook effect occurs when the antigen concentration is extremely high, such as can happen in the early stages of a disease. In this situation, there are so many antigen molecules that they can bind to both the capture and the detection antibodies, preventing the formation of the sandwich complex. As a result, the measured hormone level is much less than the actual level.

Detection

The hook effect can be detected by testing two samples from the same patient, one undiluted and the other diluted. If the measured level of the substance is higher in the diluted sample, then the hook effect may be present.

Clinical significance

The hook effect can lead to false-negative or falsely low results, causing a delay in diagnosis or treatment. It is particularly significant in pregnancy tests, where it can lead to false negatives, and in prolactin tests, where it can lead to missed diagnoses of prolactinoma.

See also

• Immunoassay
• Antibody
• Antigen
• Prolactinoma

References

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Hook_effect

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  Hook effect
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  Illustration of the effects of excess antigen and blocking antibodies on immunoassays
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  Typical Hook effect illustration