Abstract
The prompt diagnosis of active tuberculosis (ATB) is still a challenge in clinical practice, especially in TB-endemic countries. We prospectively enrolled consecutive patients with suspected pulmonary TB from two tertiary hospitals. Acid-fast staining (AFS), Xpert MTB/RIF (Xpert), Mycobacterium tuberculosis culture, and T-SPOT.TB were simultaneously performed. 226 ATB and 348 non-TB patients were diagnosed in Tongji hospital (test cohort), and 86 ATB and 110 non-TB patients were diagnosed in Guangzhou Chest Hospital (validation cohort). Using ATB as patient group and non-TB as control group, for diagnosis of ATB in Tongji Hospital, the sensitivity of AFS was 17.70% (95% CI: 13.08–23.44%). The sensitivity of Xpert and culture were 53.54% (95% CI: 46.81–60.14%) and 46.46% (95% CI: 39.86–53.19%), respectively. The sensitivity of T-SPOT.TB was 81.42% (95% CI: 75.60–86.14%), but the specificity was 71.55% (95% CI: 66.60–76.04%). Calculation of the ratio of TB-specific antigen to phytohaemagglutinin (TBAg/PHA) of T-SPOT.TB assay increased the specificity but with a loss of sensitivity. Combination of Xpert and culture slightly increased the sensitivity compared to using these methods separately. Combination of Xpert and TBAg/PHA ratio (defined as Xpert positive or TBAg/PHA ≥ 0.2) increased diagnostic accuracy, and the sensitivity and specificity of combination of them were 85.84% (95% CI: 80.45–89.98%) and 95.98% (95% CI: 93.36–97.59%), respectively. The diagnostic model was also established based on combination of Xpert and TBAg/PHA ratio. The area under the curve of the diagnostic model was 0.952 (95% CI: 0.932–0.973) for diagnosis of ATB, with a sensitivity of 88.05% (95% CI: 83.10–91.98%) and a specificity of 96.26% (95% CI: 93.70–98.00%) when a cutoff value of 0.44 was used in Wuhan cohort. The performance of combination of Xpert and TBAg/PHA ratio was similar in Guangzhou Chest Hospital. Our data suggest that combination of Xpert and TBAg/PHA ratio may be a good algorithm for prompt diagnosis of ATB in high endemic areas.
Highlights
Accurate and prompt diagnosis of tuberculosis (TB) is crucial for patient management and TB control
We hypothesized that combination of Xpert and TB-specific antigen (TBAg)/PHA ratio may be an effective way to solve this dilemma
Flexible bronchoscopy is a useful tool in diagnosing pulmonary TB, as it can be utilized to obtain respiratory samples in patients with sputum acid-fast staining (AFS) negative or who cannot expectorate sputum [22,23,24]
Summary
Accurate and prompt diagnosis of tuberculosis (TB) is crucial for patient management and TB control. None of the currently used methods can satisfy this requirement. The sensitivity of acid-fast staining (AFS) is low [1, 2]. Mycobacterium tuberculosis (MTB) culture and Xpert MTB/RIF (Xpert) assay face the same dilemma under low bacterial loads and MTB culture is limited by a long turnaround time [3,4,5]. Tuberculin skin test and T-SPOT.TB (T-SPOT) have been proven useful in detecting MTB infection [6,7,8,9]. The great limitation of these methods is their inability to distinguish active TB (ATB) from latent TB infection (LTBI) [8, 10,11,12]
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