Detection of Immunoglobulin M Antibody to Hepatitis A Virus in Patients without Acute Hepatitis A: The Usefulness of Specific Immunoglobulin G Avidity

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Abstract
Sir—The presence of IgM antibody to hepatitis A virus (HAV) is considered to be the gold standard for acute hepatitis A diagnosis. Castrodale et al. [1] report the presence of IgM antibody to HAV in persons who do not have illness meeting the case definition for acute hepatitis A in Alaska. This observation was previously published by the Centers for Disease Control and Prevention [2], along with similar cases reported from Connecticut and local health departments. Both reports suggest that test results positive for anti-HAV IgM are more likely to be false positive in older persons without typical symptoms of hepatitis. The authors recommend restricting serological testing to patients with clinical or epidemiological indication. However, because some cases of hepatitis A are asymptomatic, HAV IgM can be found without clinical symptoms or biological abnormalities [3]. In addition, authors underline that nontargeted anti-HAV IgM testing is widespread; when a clinician has to deal with a test result positive for anti-HAV IgM, the biologist cannot simply tell him, “you shouldn't have tested IgM!”