Latent TB infection can convert to active disease, especially in people with a weakened immune system that may be unable to control the latent infection. This conversion is the most common cause of active TB in the US. Therefore the focus of TB control efforts in the US is on diagnosing and treating latent TB. High-risk groups for converting typically include children, the elderly, transplant patients, people who are HIV positive, and those being treated for rheumatoid arthritis.
The only two methods for detecting latent TB infection are:
• Blood Test (e.g., The T-SPOT®.TB Test)
• Tuberculin Skin Test (TST)
Blood Test (e.g., The T-SPOT.TB Test)
Blood tests are a relatively new development in disease testing for both active disease and latent TB infections. A sample of blood is needed to run this test which is performed in the laboratory. The result of this testing is available to the doctor the next day. The T-SPOT.TB test holds several major advantages over the tuberculin skin test in that it does not require a second visit, it is not affected by BCG vaccination and it is very reliable--even in patients with weakened immune systems*.
Tuberculin Skin Test (TST)
The tuberculin skin test has been in existence for over 100 years. The test works by injecting a small amount of liquid containing TB cells into the lower part of the arm. The injection site must then be evaluated by a trained healthcare professional 48-72 hours later. If infected, the body will recognize the cells and respond by forming a lump where the TB cells were injected. The accuracy of the TST varies and can be affected by a previous BCG vaccination, a weakened immune system and by other illnesses or medical treatment.
* T-SPOT.TB Package Insert
