Given a QuantiFERON‑TB Gold test with TB‑1 antigen 1.03 IU/mL, TB‑2 antigen 0.72 IU/mL, mitogen control 8.27 IU/mL, and nil 0.17 IU/mL, what is the likelihood of Mycobacterium tuberculosis infection?

QuantiFERON-TB Gold Test Interpretation

Based on your QuantiFERON-TB Gold results (TB1-Nil = 1.03 IU/mL, TB2-Nil = 0.72 IU/mL), this test is POSITIVE for Mycobacterium tuberculosis infection, indicating a high likelihood of TB infection (either latent or active).

Test Interpretation Algorithm

Your results meet the established criteria for a positive QuantiFERON test 1, 2:

• TB1 antigen response: 1.03 IU/mL (well above the 0.35 IU/mL cutoff)
• TB2 antigen response: 0.72 IU/mL (also above the 0.35 IU/mL cutoff)
• Mitogen control: 8.27 IU/mL (adequate, confirming viable T-cells)
• Nil control: 0.17 IU/mL (acceptable background, <8.0 IU/mL)

Both TB antigen tubes exceed 0.35 IU/mL by substantial margins, and both responses are >25% greater than the nil control, satisfying all criteria for a positive result 1.

Clinical Significance

Your TB1 value of 1.03 IU/mL places you well above the "uncertainty zone" (0.2-0.7 IU/mL). Research demonstrates that individuals with interferon-gamma values >0.7 IU/mL have significantly higher rates of true TB infection 3. In fact, 87% of patients with active tuberculosis disease have values >0.7 IU/mL 3, and individuals with values >0.99 IU/mL who developed incident TB had a 0.97% progression rate within 3-24 months 4.

What This Means

• This is NOT a borderline result requiring repeat testing. Both your TB1 (1.03) and TB2 (0.72) values are definitively positive 3, 4
• The likelihood of this being a false positive is very low given both tubes are positive and values are well above cutoffs
• You have evidence of TB infection - either latent tuberculosis infection (LTBI) or potentially active disease

Critical Next Steps

1. Clinical evaluation for active TB disease is mandatory:

   • Assess for TB symptoms (cough >2-3 weeks, fever, night sweats, weight loss, hemoptysis)
   • Chest radiograph to rule out pulmonary TB
   • If symptomatic or abnormal chest X-ray: sputum cultures and molecular testing

2. If active TB is ruled out:

   • You have latent TB infection (LTBI)
   • Treatment for LTBI should be strongly considered to prevent progression to active disease
   • Risk of progression is highest in the first 2 years after infection

Important Caveats

• The TB2-TB1 difference (0.72 - 1.03 = -0.31 IU/mL) does NOT indicate recent vs. remote infection. Despite TB2 being designed to elicit CD8+ responses, research shows that TB2-TB1 differences >0.6 IU/mL do not reliably distinguish recent from remote TB exposure 5
• Your mitogen control is robust (8.27 IU/mL), confirming your immune system is functioning properly and the test is valid
• This test does not distinguish between latent and active TB - clinical and radiographic evaluation is essential 1

The positive result in both antigen tubes with values well above established thresholds indicates definite TB infection requiring clinical follow-up and consideration for treatment 1, 3.