Diagnostic usefulness of the QuantiFERON-TB gold in-tube test (QFT-GIT) for tuberculous vertebral osteomyelitis

Background: Interferon (IFN)-γ-releasing assay for diagnosing tuberculosis (TB) has shown promise; however, there are only a few reports on usefulness of the QuantiFERON-TB Gold In-Tube test (QFT-GIT) for diagnosing TB vertebral osteomyelitis. Methods: All patients presenting at a tertiary hospital between January 2010 and July 2016 with suspected TB vertebral osteomyelitis were retrospectively enrolled to evaluate the diagnostic performance of QFT-GIT. We used QFT-GIT to measure the IFN-γ response to ESAT-6, CFP-10 and TB7.7. Results: A total of 141 patients were enrolled; 32 (23%) were categorized as having confirmed TB, (1%) as probable TB, 14 (10%) as possible TB and 93 (66%) as not TB. Of these, 16 patients with probable and possible TB were excluded from the final analysis. Chronic granulomas with/without necrosis, acid-fast bacilli stain, M. tuberculosis polymerase chain reaction and cultures for M. tuberculosis were positive in 14 (44%), 12 (38%), 22 (69%) and 28 (88%) patients, respectively, among the 32 patients with confirmed TB. The overall sensitivity, specificity, positive predictive value, negative predictive value, likelihood ratio for a positive result, and likelihood ratio for a negative result of the QFT-GIT for TB vertebral osteomyelitis were 91% (95% confidence interval [CI], 75–98%), 65% (95% CI, 54–75%), 50% (95% CI, 42–58%), 95% (95% CI, 86–98%), 2.59 (95% CI, 1.89–3.55) and 0.14 (95% CI, 0.05–0.43), respectively. Conclusion: The QFT-GIT appears to be a useful adjunct test for diagnosing TB vertebral osteomyelitis because the negative test results may be useful for excluding a diagnosis of active TB vertebral osteomyelitis.