What is the role of rapid antigen detection in the workup of viral pneumonia?

Updated: Mar 24, 2021
  • Author: Zab Mosenifar, MD, FACP, FCCP; Chief Editor: John J Oppenheimer, MD  more...
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Rapid antigen detection tests provide faster results because the test is performed directly on specimens obtained from patients. Nasal swabs or washings are easy to obtain

Immunofluorescence assay and enzyme-linked immunosorbent assay (ELISA) are available for the diagnosis of HSV, RSV, influenza viruses A and B, PIV, CMV, and other respiratory viruses. ELISA can detect viral antigens, while an immunofluorescence assay requires the presence of prepared, intact, infected cells. The sensitivity and specificity of these methods varies depending on the virus being sought and the particular diagnostic assay being used.

The advantages of antigen detection tests are higher specificity for individual viruses. Furthermore, these assays remain positive for several days to weeks, long after the culture technique can detect viable virus.

The disadvantages of these methods are that the overall sensitivity is lower than that of viral cultures. Therefore, antigen detection methods should be used in conjunction with cell culture for optimal diagnosis of viral infections. [65]

RSV rapid antigen detection is useful in young children, who shed high titers of virus, but sensitivity is low in adults (0-20%) when compared with RT-PCR.

Sensitivity for seasonal influenza in adults ranges between 50% and 60%, and specificity is greater than 90%. Novel swine-origin influenza A H1N1 virus should be detectable by rapid influenza testing. However, sensitivity with rapid tests is significantly lower (51-63%) when compared with RT-PCR. Rapid influenza tests unfortunately have very poor sensitivity and specificity for the avian H5N1 influenza virus and are therefore not recommended.

With ED patients, a call to the hospital laboratory is suggested to determine the optimal test to be ordered and whether a specific viral identification should be requested or whether a general request for viral detection will result in testing for a panel of pathogens. If rapid test results are negative but clinical suspicion is high, cultures can be obtained and the patient treated until results are known. Positive viral identification cannot rule out bacterial co-infection.

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