New TB blood test could eliminate unnecessary treatment

A new screening process for tuberculosis (TB) infections in Canadian prisons could mean that more than 50 per cent of those screened won't undergo unnecessary treatment due to false positives.

According to research by Wendy Wobeser and medical resident Ilan Schwartz, a test for TB using interferon-gamma release assays (IGRA) will detect a pre-existing TB infection, or latent TB, that might not present itself for many years, or until the body becomes weakened by another source.

The IGRA test was developed in the last 10-15 years and diagnoses a latent TB infection. The body's immune system is provoked with a small amount of protein from the TB virus and if the body has previously been infected then a reaction will occur and the patient's blood will test positive for TB.

The pre-existing tuberculosis skin test (TST) for TB has been used for over 100 years but comes with two main limitations.

The current test requires two visits to determine the results: one to perform the test and then another visit a couple of days later to read the results.

Depending on the patient's exposure to other mycobacteria or the BCG vaccine, the current TB test can give many false positives.