Evaluation of a serologic test for the diagnosis of tuberculosis

The ICT TB test, a new, simple, serologic diagnostic test for tuberculosis (TB), was performed on serum samples from individuals seen at an urban teaching hospital and a local health department clinic. The study population included cases of TB, disease with mycobacteria other than tuberculosis (MOTT), non-mycobacterial pulmonary disease, and healthy controls. In contrast to prior studies, we found the ICT TB test had little value in detection of new cases of TB (overall sensitivity was 20%). It had very low sensitivity (4%) in the first month of disease. The sensitivity improved in patients tested at least 3 months after clinical presentation, but still remained fairly low. The test was also positive in 30% cases of disease caused by MOTT demonstrating cross-reactivity. It was negative in all human immunodeficiency virus (HIV) positive cases of TB or MOTT. The overall specificity was 89%. At least part of the discrepancy between our results and those of previous investigators may be attributable to differences in the respective study populations, including incidence of HIV disease and duration of tuberculosis illness prior to testing.