Review

Immunoassays are subject to interferences that are not readily detectable prior to analysis but may cause erroneous results. There are numerous reports in the scientific literature of patients receiving inappropriate medical treatment based on incorrect results of immunoassays. One case illustrating the impact of an immunoassay interference was reported in Lancet1 in the year 2000. In this case a repeated falsely high human chorionic gonadotropin (hCG) result, prompted a young woman to undergo a hysterectomy, chemotherapy, radiotherapy, and a partial pneumonectomy before the interference was discovered and her diagnosis corrected. The case was similar to a medical malpractice case reported in the Seattle Post-Intelligencer newspaper in 2001, in which a woman was awarded $15.5 million due to a misdiagnosis of cancer. In that case, fault was found with the physicians and the hospital laboratory.2 This article emphasizes the potential impact of laboratory errors in immunoassays, describes the types of interference that are specific to immunoassays, and reviews general approaches to reducing errors and associated negative outcomes in patient care. Types of Interference All laboratory assays are subject to interferences. The effects of hemolysis, lipemia, and bilirubinemia (ie, icterus) on laboratory methods, for instance, are well known. Each of these may affect the analytical measurement; good laboratory practice requires validating assays with regard to potential interferences. Because hemolysis, lipemia, and icterus produce measureable spectrophotometric changes in a serum or plasma specimen, automated chemistry analyzers routinely detect these potentially interfering substances. Thus, specimens for chemical analyses are prospectively evaluated for these potential interferences.3 Immunoassays are subject to other types of interference. Antigen-antibody interactions are the basis of immunoassays, and compounds or conditions that alter these interactions can interfere with measurement. Endogenous antibodies may bind to, bridge, or block the binding sites on capture and signal antibodies (Figure 1)