False Positive Anti-Hepatitis A Virus IgM Result in a Patient with Autoimmune Hepatitis

Abstract

This report describes a patient with autoimmune hepatitis in whom a positive test result for hepatitis A virus (HAV) IgM antibody led to diagnostic confusion until it was shown to be false positive by immunoprecipitation of IgG from serum. The mechanism for the false positive result may have been related to marked hypergammaglobulinemia, as serum obtained after normalization of immunoglobulin levels tested negative. However, several other mechanisms were also considered. This case illustrates that the possibility of false positive results with the anti-HAV lgM assay should be kept in mind when the clinical features of the illness are not suggestive of acute hepatitis A.