Perform either a Tuberculin skin test (TST) or a T-cell interferon-γ release assay (IGRA) to test for latent tuberculosis (TB) infection (LTBI) at least once after diabetes diagnosis (more often as indicated).
If the TST or IGRA test is positive, obtain a medical history, review of symptoms, targeted physical exam, and chest radiograph.
Adults with diabetes and LTBI are at high risk for progressing to active TB disease if they are not treated. Studies have shown that this risk is 2 to 6 times higher than in patients without diabetes. On average, an estimated 30% of individuals with diabetes will develop active TB disease over the course of their lifetime if they have TB infection and have not been treated. Other factors that increase the risk of progression from latent TB infection to TB disease include: intravenous drug use, immunosuppressive drugs (particularly TNF-α inhibitors) and chronic kidney disease. In most cases, progression of LTBI to active TB can be prevented with treatment.
There are two types of tests approved for LTBI testing:
Tuberculin skin test (TST). The first is the familiar tuberculin skin test. The TST was referred to previously as a purified protein derivative (PPD). In a person with diabetes, induration ≥ 10 mm 48-72 hours after administration is considered a positive result.
T-cell interferon-γ release assays (IGRA). The second type of test is the T-cell interferon-γ release assays. Two IGRA tests are currently FDA approved: the QuantiFERON®-TB Gold In-Tube test (QFT-GIT) and the T-SPOT®.TB test (T-Spot). While IGRA tests usually are more expensive than TSTs, one of their advantages is that only a single blood draw is required – patients do not have to return several days later as they do for the TST.