Is the T-SPOT (T-SPOT TB, Tuberculosis spot test) blood test more accurate than the TB Gold (QuantiFERON-TB Gold, Interferon-Gamma Release Assay) for diagnosing tuberculosis?

From the Guidelines

The T-SPOT.TB blood test is not definitively more accurate than the TB Gold (QuantiFERON-TB Gold) for diagnosing tuberculosis, as both tests have comparable sensitivity and specificity, with slight variations depending on the population and setting. When considering the diagnosis of tuberculosis, it's crucial to evaluate the sensitivity and specificity of the tests in different contexts. According to the official American Thoracic Society/Infectious Diseases Society of America/Centers for Disease Control and Prevention clinical practice guidelines 1, in individuals likely to be infected with Mtb but at low or intermediate risk of disease progression, the sensitivity of IGRAs (including T-SPOT.TB and QuantiFERON-TB Gold) has been reported as either equal or superior to the sensitivity of the TST. Some key points to consider include:

• The sensitivity of T-SPOT.TB has been reported as 90%–95%, which is superior to the sensitivity of QuantiFERON-TB Gold (81%–86%) and the TST (71%–82%) in certain populations 1.
• The specificity of IGRAs, including T-SPOT.TB and QuantiFERON-TB Gold, is generally high, with estimates suggesting that the specificity of QuantiFERON-TB Gold is >95%, whereas the specificity for TST is roughly 97% in those with no prior exposure to BCG 1.
• The choice between T-SPOT.TB and QuantiFERON-TB Gold often depends on laboratory availability, cost considerations, and specific patient factors rather than overall accuracy differences.
• Both tests represent significant improvements over the traditional tuberculin skin test by reducing false positives from BCG vaccination and requiring only a single patient visit.
• Updated guidelines for using interferon gamma release assays to detect Mycobacterium tuberculosis infection also emphasize the importance of considering the population's characteristics and the institutional setting when selecting a test 1. Ultimately, the selection of either T-SPOT.TB or QuantiFERON-TB Gold should be based on the specific clinical situation, local availability, and institutional protocols, rather than a definitive difference in accuracy.

From the Research

Comparison of T-SPOT and TB Gold Tests

• The T-SPOT test and TB Gold test are both used for diagnosing tuberculosis, but their accuracy can vary [(2,3,4,5,6)].
• A study from 2022 found that the T-SPOT.TB and QuantiFERON-TB Gold Plus tests had a high agreement of qualitative results (90%) for diagnosing latent Mycobacterium tuberculosis infection 2.
• Another study from 2006 found that the T-SPOT.TB test produced significantly more positive results (38%) compared to the QuantiFERON-TB Gold test (26%) 3.
• The QuantiFERON-TB Gold Plus test was found to have a high sensitivity (98.9%) and specificity (98.1%) for diagnosing active tuberculosis, similar to the T-SPOT.TB test 4.

Factors Affecting Test Accuracy

• The accuracy of the T-SPOT and TB Gold tests can be affected by factors such as immunosuppression, age, and BCG vaccination [(3,5,6)].
• A study from 2022 found that the use of two IGRA tests (T-SPOT.TB and QuantiFERON-TB Gold Plus) can improve the diagnosis of latent tuberculous infection in immunosuppressed patients 5.
• The T-SPOT.TB assay has been found to have better specificity than the tuberculin skin test, especially in BCG-vaccinated individuals 6.

Test Results and Discrepancies

• Discrepancies between the T-SPOT.TB and QuantiFERON-TB Gold Plus tests can occur, with one study finding a discrepancy rate of 12.43% 5.
• The T-SPOT.TB test has been found to have a lower rate of indeterminate results compared to the QuantiFERON-TB Gold test [(3,5)].
• The use of two IGRA tests can help to reduce the rate of indeterminate results and improve the accuracy of tuberculosis diagnosis 5.