Test Distinguishes Active From Latent Tuberculosis

Study finds test effective in patients where bacteria are undetectable in sputum
By A. Agrawal, PhD
HealthDay Reporter

MONDAY, Sept. 28 (HealthDay News) -- A diagnostic test using cells from bronchoalveolar lavage is quick and effective in distinguishing active tuberculosis infection from latent infection in patients with suspected tuberculosis where the bacteria are undetectable in sputum, according to a study in the Oct. 1 issue of the American Journal of Respiratory and Critical Care Medicine.

Claudia Jafari, M.D., from Research Center Borstel in Germany, and colleagues tested whether a Mycobacterium tuberculosis-specific enzyme-linked immunospot (ELISpot) assay could discriminate between sputum negative for acid-fast bacilli and latent tuberculosis infection in 347 patients with suspected tuberculosis who were unable to produce sputum or had negative smears. The test was performed on peripheral blood mononuclear cells (PBMCs) and bronchoalveolar lavage mononuclear cells (BALMCs).

The researchers found that 20.4 percent of patients had active pulmonary tuberculosis infection based on recovery of the bacteria or ruling out alternative diseases. ELISpot using BALMCs had a sensitivity of 91 percent and a specificity of 80 percent for diagnosing active infection. The BALMC ELISpot was superior in diagnosing active infection (diagnostic odds ratio, 40.4) compared with the PBMC ELISpot (odds ratio, 10.0), tuberculin skin test (odds ratio, 7.8), and M. tuberculosis-specific nucleic acid amplification (odds ratio, 12.4).

"Bronchoalveolar lavage ELISpot is an important advancement to rapidly distinguish sputum acid-fast bacilli smear-negative tuberculosis from latent tuberculosis infection in routine clinical practice," Jafari and colleagues conclude.

ELISpot test kits (T-SPOT.TB) were supplied by Oxford Immunotec Ltd. free of charge. Several authors reported financial or consulting relationships with pharmaceutical or diagnostic companies, and several authors have patents or pending patents on potential diagnostic techniques.

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