Abstract
BackgroundThe performance of the tuberculosis specific Interferon Gamma Release Assays (IGRAs) has not been sufficiently documented in tuberculosis- and HIV-endemic settings. This study evaluated the sensitivity of the QuantiFERON TB-Gold In-Tube (QFT-IT) in patients with culture confirmed pulmonary tuberculosis (PTB) in a TB- and HIV-endemic population and the effect of HIV-infection and CD4 cell count on test performance.Methodology/Principal Findings161 patients with sputum culture confirmed PTB were subjected to HIV- and QFT-IT testing and measurement of CD4 cell count. The QFT-IT was positive in 74% (119/161; 95% CI: 67–81%). Sensitivity was higher in HIV-negative (75/93) than in HIV-positive (44/68) patients (81% vs. 65%, p = 0.02) and increased with CD4 cell count in HIV-positive patients (test for trend p = 0.03). 23 patients (14%) had an indeterminate result and this proportion decreased with increasing CD4 cell count in HIV-positive patients (test for trend p = 0.03). Low CD4 cell count (<300 cells/µl) did not account for all QFT-IT indeterminate nor all negative results. Sensitivity when excluding indeterminate results was 86% (95% CI: 81–92%) and did not differ between HIV-negative and HIV–positive patients (88 vs. 83%, p = 0.39).Conclusions/SignificanceSensitivity of the QFT-IT for diagnosing active PTB infection was reasonable when excluding indeterminate results and in HIV-negative patients. However, since the test missed more than 10% of patients, its potential as a rule-out test for active TB disease is limited. Furthermore, test performance is impaired by low CD4 cell count in HIV-positive patients and possibly by other factors as well in both HIV-positive and HIV-negative patients. This might limit the potential of the test in populations where HIV-infection is prevalent.
Highlights
There is a great demand throughout the world for new methods for diagnosing both active and latent tuberculosis infection
Recent prospective studies have shown that Interferon Gamma Release Assays (IGRAs) might be more accurate and have a higher predictive value in the diagnosis of latent TB infection (LTBI) than does the conventional tuberculin skin test (TST) and a role of IGRAs in ruling out TB disease in patients suspected of TB has been proposed [2,3,4,5]
This study evaluated the performance of the QuantiFERON TB-Gold In-Tube (QFT-IT) test in a TB- and HIV-endemic population
Summary
There is a great demand throughout the world for new methods for diagnosing both active and latent tuberculosis infection. New methods for indirect tuberculosis (TB) diagnosis are available, including the Interferon Gamma Release Assays (IGRAs). In evaluation of IGRA performance active TB infection has commonly been used as a surrogate marker for LTBI, while other studies have employed risk of exposure. The performance of the tuberculosis specific Interferon Gamma Release Assays (IGRAs) has not been sufficiently documented in tuberculosis- and HIV-endemic settings. This study evaluated the sensitivity of the QuantiFERON TB-Gold In-Tube (QFT-IT) in patients with culture confirmed pulmonary tuberculosis (PTB) in a TB- and HIV-endemic population and the effect of HIV-infection and CD4 cell count on test performance
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