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Home / The International Journal of Tuberculosis and Lung Disease, Volume 20, Number 4

Using the TBAg/PHA ratio in the T-SPOT®.TB assay to distinguish TB disease from LTBI in an endemic area

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SETTING: An important limitation of the T-SPOT®.TB assay is its inability to distinguish active tuberculosis (TB) from latent tuberculous infection (LTBI).

OBJECTIVE: We proposed a new calculation method for the T-SPOT assay and assessed its effect on distinguishing active TB from LTBI.

DESIGN: A total of 162 active TB patients and 97 LTBI individuals were diagnosed according to conventional tests and the T-SPOT assay.

RESULTS: The results of early secreted antigenic target 6 (ESAT-6) and culture filtrate protein 10 (CFP-10) in T-SPOT cannot be recommended for distinguishing TB from LTBI. The number of phytohaemagglutinin (PHA) spot-forming cells (sfc) in the T-SPOT assay was reduced in active TB patients. The ESAT-6/PHA or CFP-10/PHA ratios in active TB patients were significantly higher than in individuals with LTBI. Using 0.295 as the threshold ratio of Mycobacterium tuberculosis-specific antigen (TBAg) sfc to PHA sfc (TBAg/PHA ratio, the larger of ESAT-6/PHA and CFP-10/PHA), the sensitivity and specificity were 82.1% and 90.7% in distinguishing active TB from LTBI. The TBAg/PHA ratio might also be used to monitor the effect of anti-tuberculosis treatment.

CONCLUSIONS: Calculating the TBAg/PHA ratio might have the potential to diagnose active TB and distinguish TB disease from LTBI.

Keywords: LTBI; T-SPOT; TBAg/PHA ratio; active TB

Document Type: Research Article

Affiliations: Department of Clinical Laboratory, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China

Publication date: 01 April 2016

More about this publication?

  • The International Journal of Tuberculosis and Lung Disease (IJTLD) is for clinical research and epidemiological studies on lung health, including articles on TB, TB-HIV and respiratory diseases such as COVID-19, asthma, COPD, child lung health and the hazards of tobacco and air pollution. Individuals and institutes can subscribe to the IJTLD online or in print – simply email us at [email protected] for details.

    The IJTLD is dedicated to understanding lung disease and to the dissemination of knowledge leading to better lung health. To allow us to share scientific research as rapidly as possible, the IJTLD is fast-tracking the publication of certain articles as preprints prior to their publication. Read fast-track articles.

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