Tb Test Minute Clinic (2024)

FAQs

What is a good result for TB test? ›

An induration of less than 5 millimeters (mm) is a negative result. If you have symptoms or know you've been exposed to someone with TB, a doctor may recommend you get another test. If the induration is at least 5 mm, it is considered positive in people who: have had recent contact with a person with TB.

A doctor will need to consider several things when interpreting the results of a TB test. The main consideration is the size of the bump on the arm: test bump smaller than 5 millimeters (mm), test result negative. test bump larger than 5 mm, test result in the positive range.

If a person does not return within 48-72 hours for a tuberculin skin test reading, a second test can be placed as soon as possible. There is no contraindication to repeating the TST, unless a previous TST was associated with a severe reaction.

A firm red bump may mean you have been infected with TB bacteria at some time. The size of the firm bump (not the red area) is measured 2 to 3 days after the test to find out the result. Your doctor will consider your chance of having TB when looking at the skin test site.

In people with no known risks of TB, 15 mm or more of firm swelling at the site indicates a positive reaction.

A “positive” TB blood test result means you probably have TB germs in your body. Most people with a positive TB blood test have latent TB infection. To be sure, your doctor will examine you and do a chest x-ray. You may need other tests to see if you have latent TB infection or active TB disease.

However, even use of the preferred skin test technique (intradermal injection of purified protein derivative via the Mantoux method) can lead to either false positive or false negative results.

Rarely, in highly sensitized persons, blistering or ulceration may occur. This should be brought to the attention of your health care provider for treatment. Allergic reactions can occur, but are extremely rare.

A person with a positive reaction should be referred for a medical evaluation for latent TB infection and appropriate follow-up and treatment if necessary. A measurement of 0 mm or a measurement below the defined cut point for each category is considered negative.

After the test, you should avoid using bandages, putting on lotion, or scratching the test area because it may affect the results. You can wash the area with water, but do not wipe or scrub. If the area itches, put an ice cube or cold cloth on it.

What are the odds of getting TB after exposure? ›

Between 20 to 30% of people exposed to a person with active TB become infected. For that reason, doctors usually distinguish between infection (or a positive TB test) and an active infection. After you are infected, your immune system will attack the bacteria.

What if my TB skin test is negative? The test is “negative” if there is no bump (or only a very small bump) at the spot where the fluid was injected. A negative TB skin test usually means that you don't have TB.

A positive test result means you may have been infected with TB at some point. It does not mean you have an active TB infection. The test may be seen as positive if the skin where you were injected is hard, raised, red, and swollen. But redness alone is not considered a positive test result.

Some people with inactive TB, also called latent TB infection, have a negative reaction to the TB skin test when tested years after being infected. However, if they are tested again within a year of the first test, they may have a positive reaction.

Most people with a positive TB skin test have latent TB infection. To be sure, your doctor will examine you and give you a chest x-ray. You may need other tests to see if you have active TB disease. Protect your health and the health of your family - get a TB skin test!

The reference range of the induration is 0-15 millimetres at an increment of 5 mm, 10 mm and 15 mm. An induration size of more than 15 mm is considered positive in a normal patient. A swelling of less than 4 mm is considered negative.

Countries with a TB incidence rate greater than or equal to 40 per 100,000 people.

A health care worker will use a small needle to inject testing fluid (called tuberculin) under the skin on the lower part of your inner arm. After the test, you should avoid using bandages, putting on lotion, or scratching the test area because it may affect the results.

Negative results suggest that there is not TB infection. In patients with high suspicion of exposure, a negative test should be repeated. A positive test indicates infection with Mycobacterium tuberculosis. Among individuals without tuberculosis infection, a positive test may be due to exposure to M.