The prozone phenomenon is defined as a falsely negative (=incorrectly normal) test due to very high titers (concentration) of antibody.
Many laboratory tests rely on antigen-antibody interactions. The prozone phenomenon is said to be present when dilution of a previously negative sample leads to a positive test. High levels of antigen or antibody may prevent the formation of antigen-antibody complexes.
Examples include high levels of syphilis antibodies in HIV patients or high levels of cryptococcal antigen leading to false negative tests in undiluted samples.[1][2] This phenomenon is also seen in serological tests for Brucellosis.