Endogenous interference in immunoassays in clinical chemistry. A review

The increasing availability and use of immunoassays in clinical chemistry have revealed a number of endogenous interferences. Solid-phase sandwich immunoassays based on monoclonal antibodies are particularly sensitive to any factor able to bridge immunoglobulins together. Heterophilic immunoglobulin antibodies have been demonstrated in up to 40% of patient samples and to cause spuriously elevated results unless certain precautions are taken. Rheumatoid factors belong to the same category, but their affinity is usually too low to cause significant interference. Immunoscintigraphy generates high-titre anti-immunoglobulin responses causing serious interferences in immunoassays. Recently interfering factors of unknown nature causing nonspecific binding of enzyme-labelled antibodies have been observed. Spuriously decreased values can be caused by complement, which may interfere with antigen-binding to solid phase antibody. The aforementioned and other endogenous interferences in immunoassays are reviewed and methods for their elimination discussed.