A pleural antigen assay (NOW, Binax) can supplement standard diagnostic methods for detecting pneumococcal pneumonia, Spanish researchers report in the May issue of Chest.
Dr. Jose M. Porcel of Arnau de Vilanova University Hospital, Lleida and colleagues note that in developed countries, community-acquired pneumonia is the most frequent cause of hospital admission and mortality due to infection. Streptococcus pneumoniae is often the cause.
The NOW test, the researchers note, was developed in order to provide a rapid urinary assay for detecting pneumococcal cell wall components common to all serotypes. However, testing using pleural fluid has been limited.
To investigate this approach, the researchers retrospectively used the assay with pleural fluid and urine samples from 34 patients with pneumonia due to S pneumoniae, 89 patients with effusions of non-pneumococcal origin, and 17 patients with pneumonia of unknown etiology.
The sensitivity of the NOW pleural test was higher than that obtained for blood (37.5%) and pleural fluid cultures (32.3%), but lower than the detection of pneumococcal antigen in urine samples (82.1%).
However, 3 patients with pneumococcal pneumonia and a negative NOW urine test had a positive pleural fluid antigen detection test. Furthermore, previous antibiotic exposure did not influence pneumococcal antigen detection in either pleural fluid or urine specimens.
Nevertheless, the assay provided a false positive in 6 patients without pneumococcal pneumonia, giving a specificity of 93.3%. It was also positive in 5 of the patients with pneumonia of unknown etiology (sensitivity = 70.6%).
Given these findings, the researchers conclude that this rapid immunochromatographic test used on pleural samples "augments conventional microbiological methods used for the etiologic diagnosis of pneumonia."
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