Contribution of a urinary antigen assay (Binax NOW) to the early diagnosis of pneumococcal pneumonia

Abstract

We evaluated the usefulness of a rapid urinary antigen test (Binax NOW; Binax) to detect Streptococcus pneumoniae for the early diagnosis of community-acquired pneumococcal pneumonia (PP) in 220 nonseverely immunosuppressed adults. We compared results of this test with those of sputum Gram staining. The rapid urinary antigen test showed limited sensitivity (65.9%; 95% confidence interval [CI], 51.4-80.4) but high specificity (100%; 95% CI, 99.7-100) for diagnosing PP. The test was more sensitive for patients with versus those without high-risk pneumonia (94% vs. 63%; P<.001) and for patients without versus those with demonstrative results of a sputum Gram stain (97% vs. 55%; P<.001), and it tended to be more sensitive for patients with versus those without bacteremic PP (92% vs. 74%; P=NS). Rapid urinary antigen testing permitted early diagnosis of PP in 26% more patients than did Gram staining but missed 22% of the rapid diagnoses initially identified by Gram staining. On the basis of our results, a sequential approach is proposed, with reservation of urinary antigen testing for high-risk patients for whom demonstrative results of a sputum Gram stain are unavailable.