What is the role of lab studies in the diagnosis of nocardiosis?

Updated: Jul 24, 2018
  • Author: George Kurdgelashvili, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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The diagnosis of nocardiosis is established with culture of the causative organism from the infection site(s). Because nocardiae grow slower than common bacteria, the microbiology laboratory should always be notified when nocardiosis is clinically suspected. This is particularly true when sputum is the submitted specimen. Respiratory secretions, skin biopsy samples, and aspirates from abscesses are the most common specimens from which Nocardia species are identified. Direct smears or histopathologic stains of these specimens can be highly suspicious, as noted above. Nocardia species can usually be isolated in 3-5 days.

Blood cultures are positive for Nocardia organisms in a minority of patients, but they always should be obtained when pulmonary or disseminated nocardiosis is suspected.

Immunodominant antigens of Nocardia species have been identified and used in serological assays. However, no serologic technique or molecular technique is yet available for routine clinical use. Similarly, nucleic acid amplification assays have been described but are not available for routine clinical use.

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