![]() ![]() In the past, cross-reactivity of rickettsial antibodies with Proteus OXK antigens was the basis of the Weil-Felix test used in the past for diagnosis of Rocky Mountain Spotted Fever and other rickettsial diseases. This issue is not limited to viral infections. Louis encephalitis virus and other flaviviruses. West Nile virus (WNV) is known to cross-react with St. False-positive IgM serologic results for EBV (capsid antigen) and cytomegalovirus may occur in approximately 3% of patients with acute human immunodeficiency virus infection and 30% of patients with acute hepatitis A infection. ![]() Human parvovirus infection has also been implicated in false-positive IgM assays for Epstein-Barr virus (EBV), herpes simplex virus, and HHV 6 virus infections. Subsequently, human parvovirus, rubella, and human herpesvirus (HHV) 6 infections have been described as causes of false-positive IgM test results for measles. The association of acute human parvovirus infection with false-positive measles IgM was first described in Alaska in 1994. Cross-reacting AntibodiesĬross-reacting antibodies have been described for many infections. The issue of reactivation of IgM production against herpes viruses is beyond the scope of this review. Thus, positive IgM assay results can require cautious interpretation-consideration of clinical course compatibility and epidemiological factors-and/or confirmation by other serological or molecular testing methods. Technical performance issues such as over-reading of weakly reactive bands on immunoblots can also lead to false-positive serologic tests results for microbes for which these assays are used (eg, Borrelia burgdorferi). For serologic assays, the presence of antibodies that cross-react with microbial antigens used in the assay or interfering substances that interact with assay components can also lead to false-positive results. The false-positive rate of any diagnostic test is a function of the specificity of the test and prevalence of the disease in the population represented by the patient. What are potential explanations for this? The pediatrician who ordered the test has called to ask you how this result could have happened. The family of the patient is upset about the disruption of life experienced due the false positive IgMresult. ![]() (A low positive concentration of measles IgG was detected.) The initial IgM test result has been labeled as false positive. Subsequent testing by the Centers for Disease Control and Prevention demonstrated seronegativity for measles IgM. This patient tested positive for measles IgM in a commercial assay. Two weeks ago, an adolescent who received two doses of measles-containing vaccine in childhood developed a febrile illness with rash. A measles outbreak occurred last month among a cluster of unvaccinated children in a suburban area in your referral region. ![]()
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