Tuberculosis (TB) remains a major global infectious disease caused by Mycobacterium tuberculosis, which can result in latent infection or active pulmonary and extrapulmonary disease. Early identification of latent TB infection (LTBI) is critical for preventing progression to active disease and reducing transmission.

QuantiFERON-TB Gold Plus (QFT-Plus) is an interferon-gamma release assay (IGRA) that measures cell-mediated immune response to M. tuberculosis-specific antigens in whole blood. The assay utilizes peptide antigens simulating ESAT-6 and CFP-10 proteins, which are absent from BCG strains and most non-tuberculous mycobacteria, improving specificity.

Whole blood is collected into four specialized tubes:

• Nil tube (gray): measures baseline IFN-γ background
• TB1 tube (green): detects CD4+ T-cell responseCD4+ T
• TB2 tube (yellow): detects CD4+ and CD8+ T-cell response
• Mitogen tube (purple): serves as positive immune control

Following incubation, stimulated T-cells release interferon-gamma (IFN-γ), which is quantified using an Enzyme-Linked Immunosorbent Assay (ELISA). The Nil tube accounts for background IFN-γ and nonspecific interference, while the Mitogen tube assesses overall lymphocyte function. Final interpretation is based on TB antigen responses relative to the Nil control.

• 2–8°C: up to 28 days
• ≤ −20°C: for extended storage (if required)

• Tube System: Transfer 1 mL blood into each QFT tube:
  • Nil (gray)
  • TB1 (green)
  • TB2 (yellow)
  • Mitogen (purple)
• Mixing: Invert each tube 10 times immedi

Interferon Gamma Release Assay (IGRA) with ELISA-based IFN-γ quantification

Results are based on TB antigen response relative to Nil control and Mitogen response.

Negative:
No significant IFN-γ response to TB1 or TB2 antigens.
Findings suggest no evidence of M. tuberculosis infecti

1. Pai M et al. Interferon-gamma release assays for diagnosis of latent tuberculosis infection. Lancet Infect Dis.
2. Lalvani A. Diagnosing tuberculosis infection in the 21st century. Lancet Infect Dis.
3. QuantiFERO

Back to Reproductive Immunology