From the Guidelines
The sensitivity of the QuantiFERON test for detecting latent tuberculosis infection is around 80-90%, as indicated by studies such as 1, which compared its sensitivity to the tuberculin skin test (TST) in detecting infection in persons with untreated culture-confirmed tuberculosis (TB). This interferon-gamma release assay (IGRA) measures the immune response to TB proteins in a blood sample, providing results that are generally more specific than the traditional TST. The test works by detecting the release of interferon-gamma from T-cells that have previously been sensitized to Mycobacterium tuberculosis antigens. Some key points to consider when interpreting the results of the QuantiFERON test include:
- Sensitivity may be lower in immunocompromised individuals, including those with HIV infection, patients on immunosuppressive medications, or those with malnutrition, as noted in guidelines such as 1.
- False negative results can occur in these populations, as well as in very young children and elderly patients.
- The test cannot distinguish between latent TB infection and active TB disease, so clinical evaluation is still necessary for diagnosis.
- If a patient has symptoms suggestive of active TB (such as persistent cough, weight loss, night sweats), additional testing including chest X-ray and sputum cultures should be performed regardless of the QuantiFERON result. It's also worth noting that the QuantiFERON test has been recommended for use in all circumstances in which the TST is currently used, including contact investigations, evaluation of recent immigrants, and sequential-testing surveillance programs for infection control, as stated in 1.
From the Research
Sensitivity of QuantiFERON Test
The sensitivity of the QuantiFERON test for detecting latent tuberculosis (TB) infection varies depending on the population being tested and the specific test used.
- In immunocompetent children, the sensitivity of the QuantiFERON-TB Gold In-Tube test was found to be low in infants (40%) but increased with age, reaching 77% in children aged 1-5 years and 82% in children aged 5-15 years 2.
- In immunocompromised patients, the sensitivity of the QuantiFERON-TB Gold In-Tube test was found to be lower than in immunocompetent individuals, with fewer positive results overall 3.
- In children, the QuantiFERON-TB Gold In-Tube test was found to have a sensitivity of 23% in those with positive tuberculin skin test results, although the test was highly specific 4.
- In outpatients from a TB low-endemic country, the QuantiFERON-TB Gold In-Tube test was found to be positive in 30.8% of those tested, with higher positivity rates in those with origin from a TB endemic country or previous TB disease 5.
- In diabetic patients with smear-negative tuberculosis, the sensitivity of the QuantiFERON test was found to be reduced, with a higher risk of false-negative results 6.
Factors Affecting Sensitivity
Several factors can affect the sensitivity of the QuantiFERON test, including:
- Age: Sensitivity increases with age in children 2.
- Immunocompromised status: Sensitivity is lower in immunocompromised patients 3.
- Diabetes: Sensitivity is reduced in diabetic patients with smear-negative tuberculosis 6.
- Origin from a TB endemic country: Positivity rates are higher in those with origin from a TB endemic country 5.
- Previous TB disease: Positivity rates are higher in those with previous TB disease 5.