Diagnostic usefulness of enzyme-linked immunospot assay for interferon-gamma for tuberculosis in cancer patients

The interferon-gamma enzyme-linked immunospot assay (ELISPOT) has been demonstrated to be useful in the diagnosis of active tuberculosis (TB). In this study we aimed to evaluate the diagnostic performance of the ELISPOT assay in cancer patients with suspected pulmonary TB. Eighty-one cancer patients with suspected pulmonary TB were prospectively enrolled from April 2007 to December 2008, to investigate the diagnostic sensitivity and specificity of the ELISPOT assay. Of the 38 patients with TB, 33 (86.8%) had positive ELISPOT results. Of the 43 patients without TB, the results of the ELISPOT assay were negative in 35 (81.3%) patients. The overall sensitivity was 86.8%, specificity 81.3%, positive predictive value 80.5% and negative predictive value 87.5%. No significant difference was noted for the diagnostic performance of the ELISPOT assay for diagnosing TB between solid cancer and haematological cancer patients. In addition, a quantitative study did not show that TB patients with solid cancers have a better response than haematological cancer patients as measured by spot-forming cells per 10<SU6</SU peripheral blood mononuclear cells after exposure to early secretory antigenic target 6 (ESAT-6) and culture filtrate protein 10 (CFP-10). In conclusion, the ELISPOT assay could be a useful supplementary tool for the diagnosis of pulmonary TB among cancer patients, irrespective of cancer type.