Abstract
BackgroundAs part of a formal evaluation of the Quantiferon-Gold in-tube assay (QFT-IT) for latent TB infection we compared its sensitivity to the tuberculin skin test (TST) in confirmed adult TB cases in Indonesia. Smear-positive TB disease was used as a proxy gold standard for latent TB infection.Methods and FindingsWe compared the sensitivity of QFT-IT and TST in 98 sputum smear and chest x-ray positive TB cases and investigated risk factors for negative and discordant results in both tests. Both tests showed high sensitivity; (QFT-IT; 88.7%: TST; 94.9%), not significantly different from each other (p value 0.11). Very high sensitivity was seen when tests were combined (98.9%). There were no variables significantly associated with discordant results or with a negative TST. For QFT-IT which particular staff member collected blood was significantly associated with test positivity (p value 0.01). Study limitations include small sample size and lack of culture confirmation or HIV test results.ConclusionsThe QFT-IT has similar sensitivity in Indonesian TB cases as in other locations. However, QFT-IT, like the TST cannot distinguish active TB disease from LTBI. In countries such as Indonesia, with high background rates of LTBI, test specificity for TB disease will likely be low. While our study was not designed to evaluate the QFT-IT in the diagnosis of active TB disease in TB suspects, the data suggest that a combination of TST and QFT-IT may prove useful for ruling out TB disease. Further research is required to explore the clinical role of QFT-IT in combination with other TB diagnostic tests.
Highlights
Tuberculosis (TB) remains a problem worldwide and, despite significant efforts, mortality and incidence rates remain alarmingly high [1]
While our study was not designed to evaluate the QuantiFERON-TB Gold in-tube test (QFT-IT) in the diagnosis of active TB disease in TB suspects, the data suggest that a combination of TST and QFT-IT may prove useful for ruling out TB disease
Further research is required to explore the clinical role of QFT-IT in combination with other TB diagnostic tests
Summary
Tuberculosis (TB) remains a problem worldwide and, despite significant efforts, mortality and incidence rates remain alarmingly high [1]. The QTF-IT includes three antigens, early-secreted antigen target 6 (ESAT-6), culture filtrate protein 10 (CFP-10) and TB7.7, which are absent from all BCG strains and most non-pathogenic mycobacteria [7] Comparing these tests remains a challenge in the absence of a gold standard. Test performance can be assessed indirectly by employing a gradient of exposure or by using active TB as a proxy for measuring sensitivity to LTBI [8,9] The utility of these assays for LTBI diagnosis remain unknown in Indonesia, a country that has the third highest caseload of TB disease in the world [10]. As part of a formal evaluation of the Quantiferon-Gold in-tube assay (QFT-IT) for latent TB infection we compared its sensitivity to the tuberculin skin test (TST) in confirmed adult TB cases in Indonesia. Smear-positive TB disease was used as a proxy gold standard for latent TB infection
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