Substances that might potentially alter the measurable concentration of the analyte or alter the binding ability of detection antibody can lead to immunoassay interference. Endogenous interferences consist of autoantibodies, heterophiles antibodies, human anti-animal antibodies (HAAA) and some binding proteins. Lipidemia, cross-reactivity, pre-analytical variation, matrix and different detection equipments may also affect immunoassay. These interfering substances may cause falsely increased or decreased concentration in many analytes, including hormones, tumor markers, drugs, cardiac tropanin and microbial serology, thus it will affect the diagnosis of patients and the evaluation of therapeutic strategies Laboratorians and physicians should both be aware of the potential interference in immunoassays and communicate closely when any clinical discordance between the clinical and the laboratory data appears, avoiding a subsequent wrong diagnosis and unwarranted treatment. In this case, an alternative assay or measurement is needed for the potential correct results.