Diagnostic value of the Binax NOW assay for identifying a pneumococcal etiology in patients with respiratory tract infection

Dah-Hsing Tzeng, Ya-Ling Lee, Yu-Hui Lin, Che-An Tsai, Zi-Yuan Shi
Division of Infectious Disease, Department of Internal Medicine, Taichung Veterans General Hospital, Taichung; and National Yang-Ming University, Taipei, Taiwan

Received: May 26, 2005 Revised: August 12, 2005 Accepted: August 26, 2005

Corresponding author: Dr. Dah-Hsing Tzeng, Division of Infectious Disease, Department of Internal Medicine, Taichung Veterans General Hospital, No. 160, Sec. 3, Chung-Kang Rd., Taichung 407, Taiwan. E-mail:

Background and Purpose: Streptococcus pneumoniae is a common pathogen in respiratory tract infections which is usually underestimated with conventional tests, largely due to the fragility of the bacteria. This study assessed the diagnostic value of a rapid test (Binax NOW) for the detection of the pneumococcal antigen in urine.
Methods: Unconcentrated urine samples from 1243 adults and 91 children hospitalized with respiratory tract infections were tested.
Results: In all adults with respiratory tract infections, the diagnostic results were as follows: sensitivity, 29 (60%) of 48; specificity, 748 (92.2%) of 811; negative predictive value, 748 (97.5%) of 767; false-positive rate, 63 (68%) of 92. The diagnostic results were similar in adults with lower respiratory tract infections: sensitivity, 21 (64%) of 33; specificity, 658 (92.2%) of 714; negative predictive value, 658 (98.2%) of 670; false-positive rate, 56 (73%) of 77. In children with respiratory tract infections, the diagnostic results were: sensitivity, 4 of 4; specificity 18 (64%) of 28; negative predictive value, 18 of 18; false-positive rate, 10 of 14. The low specificity of the test in children may be due to frequent pneumococcal nasopharyngeal colonization.
Conclusions: High negative predictive values and high false-positive rates were found in both adults and children, indicating that a negative result may be more useful than a positive one in clinical practice. The high specificity of this test in adults indicates its potential value in the choice of initial antibiotic treatment by eliminating pneumococcal infection as a likely cause of respiratory tract infection in a proportion of patients.

Key words: Bacterial antigens, diagnostic reagent kits, predictive value of tests, sensitivity and specificity, Streptococcus pneumoniae

J Microbiol Immunol Infect 2006;39:39-44.