Search

The potential for interfering substances to cause inaccurate laboratory results that may cause significant adverse effects on patient care is well known. Immunoassays are subject to interferences that are not readily detectable prior to analysis, but may cause erroneous results. Learning Objectives After reading this article, readers should understand potential causes of interference that are specific to immunoassays, methods used to detect interference, and approaches used to resolve discrepancies between laboratory results and the clinical picture. [ABSTRACT FROM AUTHOR]

A patient with IgA deficiency had a series of positive serum pregnancy tests which led to medical and surgical procedures for suspected molar pregnancy. These tests were found to be falsely positive due to heterophile antibody. The aim of this study was to determine the frequency of false positive βhCG assays in sera of IgA deficient patients. Sera from a panel of IgA deficient (IgA < 7 mg/dl) patients were tested for the presence of βHCG using three different assays, and also for IgG anti-goat and anti-mouse antibodies. Patients were seen at Mount Sinai Medical Center and included 54 patients (ages 1–80 years, 32 females, 22 males) with IgA deficiency. Thirty percent of 54 IgA deficient patient sera yielded positive pregnancy tests by one or more of the three βhCG assays, however, none of the patients were pregnant. In comparison to sera of normal controls, 39% of the patient sera contained significant amounts of anti-goat antibody and 18% contained significant amounts of anti-mouse antibody. While heterophile antibodies are common in IgA deficient serum, false positive assays for βhCG in IgA deficient serum have not been previously reported. The possibility of false positive test results should be considered prior to invasive procedures in IgA deficient patients. [ABSTRACT FROM AUTHOR]

The heterophile antibody (Monospot), initial test of choice for Epstein-Barr virus (EBV)-associated infectious mononucleosis, is both sensitive (70-92%) and specific (96-100%). False positives have been demonstrated in cases of viral hepatitis, human immunodeficiency virus, leukemia, lymphoma, pancreatic cancer, systemic lupus erythematosus, and rubella. We present a case of a 46-yr-old male who developed fever, chills, headaches, myalgia, fatigue, and photophobia 1 d after returning from the Philippines. He demonstrated a mild transaminitis and significant thrombocytopenia (12,000 cells/μL). His initial evaluation revealed a positive heterophile antibody test. Without a classic EBV presentation, a fever in returning traveler evaluation was instituted resulting in a positive dengue test by direct fluorescence IgM (8.82 IU) and IgG (7.13 IU), respectively. Both his EBV DNA polymerase chain reaction and IgM by viral capsid antigen were negative. Dengue, an RNA flavivirus, and the dengue antibody have demonstrated cross-reactivity with other flaviviruses including Japanese encephalitis virus, yellow fever virus, West Nile virus, and St. Louis encephalitis. However, EBV is a double-helix DNA herpesvirus and structurally very different. To our knowledge, this is the first reported case of cross-reactivity between dengue and EBV that describes a potential false positive for the heterophile antibody test. [ABSTRACT FROM AUTHOR]