Diagnostic Performance of an Enzyme-Linked Immunospot Assay for Interferon-Gamma in Extrapulmonary Tuberculosis Varies between Different Sites of Diseases

Abstract

OBJECTIVES: To evaluate diagnostic performance of an enzyme- linked immunospot assay for interferon-gamma (T SPOT-TB) in patients with suspected extrapulmonary tuberculosis (TB). METHODS: From January 2007 to December 2008, patients with suspected extrapulmonary TB were prospectively enrolled from 2 tertiary care hospitals. RESULTS: A total of 138 patients with suspected extrapulmonary TB were enrolled; 50 patients had positive culture for Mycobacterium tuberculosis and 39 patients had probable TB. The sites of infection were lymph node (n = 20), pleura (n = 19), bone/joint (n = 15), urinary tract (n = 7), peritoneum (n = 7), meninges (n = 6), disseminated (n = 5), intestine (n = 3), pericardium (n = 2) , skin (n = 2), throat (n = 1), neck (n = 1), and genitalia (n = 1). The overall sensitivity and specificity were 79.8% (71/89) and 81.6% (40/ 49). The sensitivity ranged from 100% for tuberculous meningitis, tuberculous pericarditis, and intestinal TB, 95% for lymphadenitis, to 42. 9% for tuberculous peritonitis. The sensitivity of the T SPOT-TB assay was 70.6% in immunocompromised patients and 85.5% in immunocompetent patients (p = 0.09). CONCLUSIONS: The T SPOT -TB assay can be a useful tool for diagnosing extra- pulmonary TB in immunocompetent and immunocompromised patients, particularly for tuberculous meningitis, pericarditis, lymphadenitis, and intestinal TB.