Serologic diagnosis of tuberculosis using a simple commercial multiantigen assay

Seven primary health clinics and a pulmonary disease specialty clinic in Rio de Janeiro City, Brazil.

To evaluate a commercial immunochromatographic test kit (ICT Tuberculosis; AMRAD-ICT; Sidney, Australia) employing five recombinant Mycobacterium tuberculosis proteins for the detection of pulmonary tuberculosis (TB).

Serology test results were compared with duplicate sputum microscopy and culture in 277 patients with symptomatic pulmonary disease (243 with pulmonary TB and 34 with nontuberculous disease). An additional 110 healthy control subjects were also tested.

The serology test was simple and rapid to perform and detected 64.2% of smear-positive and 46.3% of smear-negative TB patients overall. HIV co-infection was present in 15.3% of TB patients, and serology was much less sensitive (overall 27.6%) in this small group, as was microscopy (13.8%). Specificity of the serology test was 100% in healthy control subjects and 85.2% in the small number of control patients with pulmonary disease, including those with prior TB. Combined with microscopy, serology detected 72.8% of TB patients.

Depending on the population studied, multiantigen serologic tests for TB may be as sensitive as microscopy, but detect a different and overlapping subset of patients. The use of multiple antigens in this kit increased test sensitivity without significant loss of specificity. Bacille Calmette-Guérin vaccination and tuberculin sensitivity did not affect serology results. Estimating specificity in clinical use will require testing a much larger cohort of symptomatic patients with nontuberculous disease. The TB diagnostic performance of this group of antigens in HIV co-infected individuals was poor.