Enzyme-linked immunospot assay for interferon-gamma to support the diagnosis of tuberculosis in diabetic patients

The aim of this study was to evaluate the support to tuberculosis diagnosis of a new immunological tool, an enzyme-linked immunospot (ELISPOT) assay for interferon-γ, in diabetic patients. From March 2007 to January 2008, diabetic patients with suspected pulmonary tuberculosis were enrolled in a tertiary care hospital. Data on clinical characteristics of the patients and conventional laboratory results were collected and blood samples were obtained for ELISPOT assay (T SPOT-TB; Oxford Immunotec Ltd, Oxford, UK). A total of 84 patients with suspected pulmonary tuberculosis were recruited. Fifty-one (60.7%) of these patients were considered to have pulmonary tuberculosis, including 42 (50%) with confirmed tuberculosis and 9 (10.7%) with probable tuberculosis. The overall (confirmed and probable tuberculosis) sensitivity, specificity, positive predictive value and negative predictive value of the ELISPOT assay were 84.3%, 66.7%, 79.6%, and 73.3%, respectively. The negative predictive value of the ELISPOT assay was significantly higher in patients with adequate glycaemic control (90% vs 56.3%). In conclusion, the ELISPOT assay can provide useful support in diagnosing pulmonary tuberculosis in diabetic patients, especially those with adequate glycaemic control.