Mycoplasma pneumoniae Antibodies, IgM

The Mycoplasma pneumoniae Antibodies, IgM assay (anti-Mycoplasma pneumoniae IgM) serves as an aid in diagnosing acute M. pneumoniae infection and in distinguishing atypical pneumonia from illnesses caused by other respiratory pathogens, including streptococci and staphylococci. Interpretation is strengthened when assessed alongside IgG serology demonstrating seroconversion or a rising titer, the clinical presentation, and, when appropriate, nucleic acid amplification testing.

Mycoplasma pneumoniae is a common cause of community-acquired atypical pneumonia. Clinical features often include a persistent nonproductive cough, fever, pharyngitis, headache, and myalgia. The humoral response includes an early rise in pathogen-specific IgM, which typically appears within the first weeks of symptoms and can persist for several months. Because IgM may reflect acute or recent infection, correlation with serial IgG results showing seroconversion or an increasing titer and, when indicated, nucleic acid amplification testing improves diagnostic confidence. Positive M. pneumoniae IgM can occur in the context of infections due to mycoplasma species other than Mycoplasma pneumoniae or with Ureaplasma infection. These potential sources of cross-reactivity or nonspecific reactivity should be considered when interpreting isolated IgM results.