[Clinical usefulness of T-SPOT.TB test for the diagnosis of tuberculosis]

The risk of tuberculosis in Korean patients with inflammatory bowel disease receiving tumor necrosis factor-α blockers

The aims of this study were to assess the risk of tuberculosis (TB) and the status of latent tuberculosis infection (LTBI) in Korean patients with inflammatory bowel disease (IBD) receiving tumor necrosis factor (TNF)-α blockers. We reviewed medical records of 525 Korean IBD patients (365 TNF-α blocker naïve and 160 TNF-α blocker exposed) between January 2001 and December 2013. The crude incidence of TB was significantly higher in IBD patients receiving TNF-α blockers compared to TNF-α-blocker-naïve patients (3.1% vs. 0.3%, P=0.011). The mean incidence of TB per 1,000 patient-years was 1.84 for the overall IBD population, 4.89 for TNF-α blocker users, and 0.45 for TNF-α-blocker-naïve patients. The adjusted risk ratio of TB in IBD patients receiving TNF-α blocker was 11.7 (95% confidence interval, 1.36-101.3). Pulmonary TB was prevalent in patients treated with TNF-α blockers (80.0%, 4/5). LTBI was diagnosed in 17 (10.6%) patients, and none of the 17 LTBI patients experienced reactivation of TB during treatment with TNF-α blockers. Treatment with TNF-α blockers significantly increased the risk of TB in IBD patients in Korea. De novo pulmonary TB infection was more prevalent than reactivation of LTBI, suggesting an urgent need for specific recommendations regarding TB monitoring during TNF-α blocker therapy.

[Analysis of patients with positive acid-fast bacilli culture and negative T-SPOT.TB results]

BACKGROUND

T-SPOT.TB is a sensitive test that detects interferon-gamma producing T-cells in tuberculosis patients following stimulation with tuberculosis-specific antigens. Our study was aimed to investigate the possible causes of false negative results of the test by analyzing the patients with positive acid-fast bacilli (AFB) culture and negative T-SPOT.TB results.

METHODS

We investigated 138 patients with positive AFB culture results reported between January 2009 and April 2010. Medical records of these patients were reviewed for the results of T-SPOT.TB test, AFB culture, PCR for Mycobacterium tuberculosis (TB-PCR), chest X-ray, drug treatment, etc. Diagnosis of tuberculosis was confirmed by positive TB-PCR or identification of Mycobacterium tuberculosis (MTB). Sensitivity of T-SPOT.TB test was calculated and the possible causes of AFB culture positive and T-SPOT.TB negative results were analyzed.

RESULTS

T-SPOT.TB test was performed in 63 of the 138 patients with AFB culture positive results. Fifty-six (88.9%) were positive and 7 patients (11.1%) were negative on T-SPOT.TB test. Of these 7 negative cases, 4 were confirmed as nontuberculous mycobacteria (NTM), 2 were suspected as NTM and diagnosis could not be confirmed in 1. Six of these 7 patients were over 70 yr old and 6 patients had lymphocytopenia. T-SPOT.TB negative results were not observed in any of the 44 patients confirmed to have active tuberculosis (sensitivity 100%).

CONCLUSIONS

Our results suggest that T-SPOT.TB test is very sensitive for diagnosing active tuberculosis. NTM may be the main cause of AFB culture positive and T-SPOT.TB negative results, but MTB infection in immunocompromised patients also has to be considered.