Positive TB test: Am I sick?

Dear Alice,

What does a positive result of a TB test mean? Once a person is positive, is that going to be positive for the rest of his/her life?

— Air-borne

Dear Air-borne,

TB or not TB: that is the question! A person who tests positive for tuberculosis (TB) has likely been exposed (at some point in their lives) to either Mycobacterium tuberculosis (the organism that causes infectious TB) or protein from the bacterium. So yes, once exposed, a person will always have a positive test that reflects the history of that exposure. However, a positive test doesn’t necessarily mean that they’ll have an active infection — there are several situations in which someone might test positive without ever having symptoms (more on that later). While a positive TB test might naturally conjure up alarming images, it might also reassure you to know that modern treatment options are available. 

First, it might be helpful to clarify that there are two different types of TB tests: the tuberculin skin reactivity test (also called the Mantoux Test) and the TB blood test. The skin test will help to determine whether a person has ever been exposed to the TB protein by injecting a small bubble of fluid with purified TB protein (which doesn’t cause illness) into the skin of the forearm. A health care provider then "reads" the site of injection for signs of a positive reaction 48 to 72 hours later. The TB blood test, on the other hand, measures whether a person’s white blood cells will react to TB bacteria. A positive blood test indicates that a person is either currently infected or has been infected with TB bacteria in the past. A follow-up chest x-ray or sputum culture may need to be completed to confirm a positive result from either the skin or the blood test.

Here are some potential explanations for a positive TB test:

The Bacilli Calmette-Guerin (BCG) Vaccine: The BCG vaccine works against two specific forms of TB: childhood tuberculosis meningitis (TB in the central nervous system) and military disease (TB that causes lesions throughout the body). Many people who have lived in countries with a very high risk of TB exposure have been vaccinated — these individuals will likely get a positive skin reactivity test, even if they've never actually been exposed to a TB infection. For this reason, sometimes a TB blood test is preferred for people who’ve had the vaccine to get the most accurate results.

Latent tuberculosis: In most cases, when generally healthy people are exposed to the TB bacteria, the body’s immune system does a good job of preventing the bacteria from causing illness. In cases where the body does not effectively get rid of the TB infection entirely, the TB bacteria may remain in the body in a dormant, inactive state. People with this latent form of TB don't have symptoms and can’t spread the disease to others, but may present a positive on either TB test.

Tuberculosis disease: If the body's immune system is unable to keep the bacteria in check, the infection can result in active tuberculosis. People with active TB usually have one or more symptoms of the disease and may be very contagious to others. While TB typically affects the lungs, the brain, kidneys, spine, and other organs can also be affected. General symptoms include:

  • Feeling weak or sick
  • Loss of appetite
  • Unexplained weight loss
  • Fever
  • Chills
  • Night sweats

Specific symptoms of the infection in the lungs include a cough that lasts three or more weeks, which may be bloody or accompanied by chest pain. The symptoms experienced from TB in other parts of the body will depend on the specific organs affected.

So how does someone get exposed to this bacterium in the first place? Tuberculosis can be spread through droplets in the air when someone with an active infection coughs or sneezes. Certain factors can increase the chance of being exposed to TB bacteria, including:

  • Spending time in close contact with someone who has infectious (not latent) TB.
  • Living or working in a high-exposure setting, such as a correctional facility, long-term care facility, homeless shelter, or in hospital and clinical health care settings.
  • Having recently traveled to areas of the world where TB is common.

The Centers for Disease Control and Prevention (CDC) recommends that anyone in these high-risk settings be tested, especially if they’re experiencing TB-like symptoms.

While this disease can be fatal if left untreated, the good news is that treatment is available for both latent and active TB. A health care provider may prescribe antibiotics for individuals with latent TB to clear out any existing inactive bacteria and prevent them from causing disease. For those with active TB, several different antibiotics will likely be provided to treat the infection. It’s highly recommended that these medications be taken exactly as prescribed until the full course of treatment is complete — even if symptoms start to go away sooner. Otherwise, it’s possible that the bacteria become drug-resistant, making the disease even more difficult to treat and cure in the future.

If you or someone you know has tested positive for TB, consider making an appointment with your health care provider to get a confirmed diagnosis and determine your next steps. Additionally, you may want to talk to your provider if you use certain types of birth control as some of the antibiotics used to fight TB infection may interfere with hormonal birth control. Once you receive your test results, it may be helpful to save these documents; you may later be requested to submit copies to your health care provider, employer, or school.

Hope this helps your knowledge about TB tests increase from a deficit to a positive!

Last updated Dec 16, 2016
Originally published Oct 01, 1994