Prozone Effect Definition

Prozone effect, or hook effect, is a potentially troublesome phenomenon in antibody-antigen laboratory testing. False negative or false low results occur from the excess of antigen or antibody in a sample due to the inability of the analyte to bind to receptor sites.

How It Occurs

• In a typical immunoassay, antigens and antibodies bind to create a conjugate, which is detected and measured. When prozone effect occurs, excess antigens or antibodies bind all of the receptor sites, leaving nothing available to become a conjugate. No conjugate is detected, and a false negative result is produced.

How To Detect

• A false negative result could easily be undetected unless the clinician or researcher responsible for ordering the test strongly suspects or knows that the result should be positive. To detect prozone effect, the sample should be diluted and retested. If the result is positive, prozone effect occurred.

How To Avoid

• Unless you already know the sample is strongly positive, prozone cannot be avoided. Many laboratories enlist a protocol to confirm negative results by dilution or testing via another method, such as a culture. These protocols commonly are used for testing, such as for syphilis and legionella.