What is the best screening test for Tuberculosis (TB)?

From the Guidelines

The best screening test for tuberculosis is the interferon-gamma release assay (IGRA) blood test, which is preferred over the tuberculin skin test (TST) due to its higher specificity and lower interference from treatment with glucocorticoids, DMARDs, or immunosuppressants. According to the most recent guidelines from 2023, IGRA performs better than TST in the diagnosis of latent TB and is less affected by prior treatments 1. The IGRA blood tests, such as QuantiFERON-TB Gold or T-SPOT.TB, measure the immune response to TB proteins in a blood sample and are more specific than TST, especially in individuals with prior BCG vaccination.

Some key points to consider when choosing a screening test for tuberculosis include:

• The IGRA test is preferred over TST due to its higher specificity and lower interference from prior treatments 1
• The TST requires intradermal placement of tuberculin purified protein derivative and interpretation of skin erythema and induration response 48–72 h later 1
• Both IGRA and TST have their own limitations and patient factors, such as prior BCG vaccination, may influence the selection of a screening test 1
• Guidelines from various organizations, including the WHO, USPSTF, ATS, CDC, and IDSA, support testing with IGRA over TST for diagnosis of latent TB in individuals with low-to-intermediate risk of progression to active disease 1

It is also important to note that a chest X-ray may be included in the TB-screening procedures, especially as a negative IGRA or TST cannot exclude active TB or rule out latent TB 1. Overall, the choice of screening test for tuberculosis should be based on individual patient factors, risk of progression to active disease, and the availability of testing options.

From the Research

Screening Tests for Tuberculosis

• The tuberculin skin test (TST) and interferon-gamma release assays (IGRAs) are commonly used for the diagnosis of latent tuberculosis infection (LTBI) 2, 3, 4, 5, 6.
• Australian guidelines recommend the TST as the preferred test for LTBI, with IGRA as a supplemental test to improve specificity 2.
• IGRAs, such as T-SPOT.TB and QuantiFERON-TB Gold In-Tube, have been shown to be more sensitive and specific than TST for the diagnosis of TB infection 3, 4.
• A systematic review and meta-analysis found that IGRAs had a better predictive ability than TST for the progression of latent infection to active tuberculosis disease 5.
• The use of a combination of TST and IGRA may improve detection of LTBI, especially in high-risk populations 5, 6.

Comparison of TST and IGRA

• Studies have shown that IGRAs are more sensitive and specific than TST for the diagnosis of TB infection, especially in BCG-vaccinated populations 3, 4, 6.
• The TST has a higher false-positive rate than IGRA, especially in populations with a high prevalence of BCG vaccination 3, 6.
• IGRA positivity has been associated with the level of exposure to TB, and IGRA positivity and the level of exposure are risk factors for TB incidence 6.

Recommendations

• The choice of screening test for TB infection should be based on the individual's risk factors, such as exposure history and BCG vaccination status 2, 5, 6.
• IGRAs may be preferred over TST in populations with a high prevalence of BCG vaccination or in individuals with a high risk of TB exposure 3, 4, 6.
• A combination of TST and IGRA may be used to improve detection of LTBI, especially in high-risk populations 5, 6.