Which tests are used to identify the etiology of viral pneumonia?

Updated: Mar 24, 2021
  • Author: Zab Mosenifar, MD, FACP, FCCP; Chief Editor: John J Oppenheimer, MD  more...
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Viral cultures are still the criterion standard for most viral pathogens, but they take a long time to complete. Therefore, methods faster than this have been introduced. Viral-antigen detection is one of the new tests, but the results are generally less sensitive and less specific than those of conventional cell cultures.

Viral nucleic material amplification, such as hybridizations, various polymerase chain reactions (PCRs), [64] and serologic tests, can be used to follow the increase in specific serum antibodies and for diagnostic purposes.

Recent interest has focused on developing PCR-based tests with single, multiplex, and real-time readings. These tests have sensitivity better than that of cultures.

Nested PCR and reverse-transcriptase (RT) PCR are the most sensitive methods. They increase the detection rate of respiratory viruses in adults with hematologic cancers and pneumonia from 19% to 35%.

PCR is limited by the fact that the results cannot completely rule out contamination of the specimens. In some immunocompromised patients, who shed the virus for long periods, the diagnosis can be of little clinical significance. This limitation is overcome by using quantitative PCR, which shows the level of viral load. The findings can also help in differentiating active infection from contamination.

Because of the difficulty in distinguishing between the various etiologic agents, both viral and bacterial, causing pneumonia, the workup for symptomatic patients with an infiltrate on chest radiograph should include laboratory studies.

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