Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1413 page)

   DFA: Specimens showing a significant number of cells with 2+ or greater fluorescence are considered positive, establishing a diagnosis of influenza in patients with compatible signs and symptoms. Slides must be examined to ensure that the specimen contains enough respiratory epithelial cells to provide informative testing. Laboratories should establish a lower limit of cells present below which the test is considered uninterpretable. Specimens that demonstrate only few, faintly staining cells should be considered equivocal; repeat testing may provide clear positive or negative results.

   
Negative results:

   
EIA:
A negative result does not exclude respiratory virus infection.

   
DFA:
A cellular specimen without staining by the labeled reagent is reported as negative. Infection with the specific viral pathogen is unlikely.

   Limitations

   The sensitivity for different commercially available EIA tests is variable. Sensitivities commonly range from 50% to 80%. Clinically, test performance depends on the type of specimen and quality of specimen collection. Only specimen types acceptable for the kit, collected according to kit instructions, should be accepted.

   The PPV of antigen detection tests depends on the prevalence of viral pathogen in the region. Testing results should be interpreted with caution, if performed at all, during periods when there is a low prevalence of the pathogen circulating in the region.

   
Common pitfall:
Poor test performance may be seen when specimens are submitted that have not been validated for the platform/kit used for testing. Anterior nasal swabs, for example, may be submitted instead of nasopharyngeal swabs, resulting in an increased number of false-negative results.

RESPIRATORY VIRUS PANEL (RVP) MOLECULAR ASSAY
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   Definition

   The RVP assay is a comprehensive panel of tests for the detection of multiple viral strains and subtypes. Various molecular assays differ in the specific list of respiratory viruses tested, but most include influenza A (and subtypes), influenza B, parainfluenza, adenovirus, metapneumovirus (HMPV), RSV, and rhinovirus.

   
Normal range:
Not detected.

   Use