Utility of pneumococcal urinary antigen detection in diagnosing exacerbations in COPD patients

The aim of this study was to evaluate the utility of pneumococcal urinary antigen detection (Binax Now Streptococcus pneumoniae Antigen Test) in diagnosing pneumococcal exacerbation of chronic obstructive pulmonary disease (COPD). Forty-six patients with S. pneumoniae isolation in sputum culture were studied (29 collected in stable period and 17 collected during exacerbation). In the 29 patients with samples collected in a stable period the antigen was detected in 3 cases (10.3%) using nonconcentrated urine (NCU), and in 12 cases (41.4%) using concentrated urine (CU). Regarding patients recruited during an exacerbation period, the antigen was detected in 3 cases (17.6%) using NCU, and in 13 cases (76.5%) when CU was used. For the evaluation of the specificity of the ICT test we also tested 72 cases in which pneumococcus was not isolated in the sputum sample. ICT was positive in 1NCU and 9CU of these patients. To have had at least one previous exacerbation (P=0.024), at least one exacerbation that required hospitalization (P=0.027), and a pneumonia episode in the year before (P=0.010) had statistically significant associated with the detection of specific antigen in CU. Using NCU, the only significant association was found when a previous pneumonia in the year before had occurred (P=0.006). In summary, a positive result of pneumococcal urinary antigen from a COPD patient, in both bronchial exacerbation and pneumonia, should be evaluated with caution because the antigen detected could be related with previous infectious episode.