What is the role of urinary antigen testing in the diagnosis of Legionnaires disease?

Updated: Aug 24, 2018
  • Author: Burke A Cunha, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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The Legionella lipopolysaccharide antigen is detected with ELISA, radioimmunoassay (RIA), and the latex agglutination test. The Legionella lipopolysaccharide antigen becomes detectable in 80% of patients on days 1-3 of clinical illness. The urinary antigen assay can be used to detect only L pneumophila (serogroup 1). [11]

The advantages of urinary antigen testing include rapidity and simplicity. In addition, the relative ease of obtaining a urine sample compared with obtaining sputum specimens and the persistence of antigen secretion in patients who are on antibiotic therapy increase the usefulness of the urine antigen detection method. [11]

The urinary antigen test may initially be negative, but when positive it can remain positive for months after the acute episode has resolved. [11]

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