Inadequate values from an interferon-gamma release assay for smear-negative tuberculosis in a high-burden setting

Area of Science:

• Medical Diagnostics
• Infectious Diseases
• Respiratory Medicine

Background:

• Tuberculosis (TB) diagnosis in China remains challenging, particularly for smear-negative pulmonary TB.
• Interferon-gamma release assays (IGRAs) like T-SPOT.TB offer an alternative diagnostic approach.
• Evaluating IGRA utility in specific populations, like Chinese patients with presumed pulmonary TB, is crucial.

Purpose of the Study:

• To assess the diagnostic performance of T-SPOT.TB for smear-negative pulmonary tuberculosis in China.
• To compare the sensitivity and specificity of T-SPOT.TB in smear-negative versus smear-positive TB patients.
• To determine the clinical utility of T-SPOT.TB as a standalone or supplementary diagnostic tool.

Main Methods:

• Prospective enrollment of 624 patients with suspected pulmonary TB.
• Classification of patients into smear-negative TB, smear-positive TB, and no TB groups.
• Testing all patients with the T-SPOT.TB assay to measure spot-forming cells (SFCs).

Main Results:

• Both TB groups showed significantly higher SFCs than the no TB group (P < 0.001).
• T-SPOT.TB demonstrated a sensitivity of 81.4% for smear-negative TB and 93.2% for smear-positive TB.
• Specificity was 60.4%, with lower sensitivity observed in smear-negative TB patients compared to smear-positive TB patients (P < 0.05).

Conclusions:

• Lower sensitivity in smear-negative TB is attributed to the paucibacillary nature of samples.
• Reduced specificity is linked to a high prevalence of latent tuberculous infection among smear-negative patients.
• T-SPOT.TB should be utilized as an adjunct diagnostic test, not a definitive standalone test for smear-negative TB.