Blood test reveals latent tuberculosis

Dear Dr. Roach: Ihada tuberculosis (TB) skin test for my new job in May, and it was negative. They did a blood test in July. I have a question about a positive T-SPOT blood test for TB. They did a chest X-ray, and it shows nothing wrong. Is there any treatment necessary?

I haven’t been told of any, but from what I read, it could be latent TB, which means it’s just silent but can show up at any time. Does this mean that I came into contact with TB and my body just fought it off, or could this be a false positive? Any help would be great.

A.M.

Answer: The T-SPOT, like the QuantiFERON-TB Gold, is a blood test to look for tuberculosis infection. “Active” tuberculosis and “latent” tuberculosis are different, and the blood tests will be positive in both active and latent TB. Active tuberculosis commonly causes cough, fatigue and weight loss. A chest X-ray is abnormal in virtually all cases of active tuberculosis: Since yours is negative, it’s very likely you have latent tuberculosis. Both blood tests are more accurate than the TB skin test.

Latent infection means the tuberculosis bacteria are still alive inside you, but kept in check by your immune system. Unfortunately, due to illness, stress or just getting older, sometimes latent infections can escape the immune system and become active infections. Roughly 8% of people with latent TB will develop active TB during their lifetimes, but it’s most common within a few years of acquiring the latent infection.

People of any age who recently acquired latent TB are at high enough risk for active TB that they are recommended to receive treatment. This is intended to kill all the latent TB bacteria and reduce the likelihood of developing active TB later. Treatment is highly effective, with most studies showing only about a 1% lifetime chance of developing active tuberculosis after completing treatment for latent TB.

There are both one-drug and two-drug regimens for latent TB. The most commonly used regimen now is probably rifamycin for four months.

People who have a positive test without a recent negative test are also usually treated.