Testing for Tuberculosis: Skin Test (2024)

FAQs

How to read TB skin test results? ›

If you have an Mtb infection, the skin around the injection site should start to swell and harden within 48 to 72 hours . This bump, or induration, may also change color. But the induration's size, not the color, will determine your results. An induration of less than 5 millimeters (mm) is a negative result.

Normal Results

A negative reaction usually means you have never been infected with the bacteria that cause TB. With a negative reaction, the skin where you received the PPD test is not swollen, or the swelling is very small.

Your health care provider MUST check your arm 2 or 3 days after the TB skin test, even if your arm looks OK to you. If you have a reaction to the test, it will look like a raised bump. Your health care provider will measure the size of the reaction. If there is a bump, it will go away in a few weeks.

Results. Redness alone at the skin test site usually means you haven't been infected with TB bacteria. 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.

A TB skin test detects if a patient has ever been infected with TB but does not determine if a patient currently has TB infection or TB disease. Further testing is required to confirm or rule-out a diagnosis of TB disease.

After the test, you should avoid using bandages, putting on lotion, or scratching the test area because it may affect the results.

The area where the skin test was given will be examined for a reaction. The nurse will measure this reaction; the TB skin test is positive if the reaction is 10mm or larger. In certain situations, we use 5mm as a positive test. Your health care practitioner will explain your result.

A tuberculin skin test may be applied on the same day as routine immunizations. The skin test will need to be read 48-72 hours later.

If there is no reaction after 2-3 days, you most probably have not been exposed to the TB germ. If there is a reaction, some redness and a small bump will appear on the arm. A measurement of 10 millimetres or more is "positive", and means you may have the TB germ in your body.

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.

What if my TB test is red but no bump? ›

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. In many cases, a healthy immune system will surround the TB bacteria soon after you are infected.

The tuberculin skin test must be given and read by a professional who has been trained to do this, and has been informed of the most recent guidelines in tuberculosis control. Never allow anyone other than a nurse or physician to read a tuberculin skin test.

Results will not be available on the same day you have the test. You must return to the healthcare provider 48-72 hours after the test is administered to have the results read and receive the required form.

Fifteen mm or more is positive in

Persons with no known risk factors for TB. Reactions larger than 15 mm are unlikely to be due to previous BCG vaccination or exposure to environmental mycobacteria.

Some persons may react to the TST even though they are not infected with M. tuberculosis. The causes of these false-positive reactions may include, but are not limited to, the following: Previous TB vaccination with the bacille Calmette-Guérin (BCG) vaccine.

Side effects are uncommon from the Mantoux skin test. However, a person who has been exposed to TB germs may occasionally have a sizable reaction, which may cause some mild itching, swelling or irritation. These kinds of reactions should disappear in one to two weeks.

You don't any special preparations for TB skin test or a TB blood test.

Your health care provider MUST check your arm 2 or 3 days after the TB skin test, even if your arm looks OK to you. If you have a reaction to the test, it will look like a raised bump. Your health care provider will measure the size of the reaction. If there is a bump, it will go away in a few weeks.

A measurement of 0 mm or a measurement below the defined cut point for each category is considered negative.

Can a TB skin test be injected wrong? ›

However, the following factors may cause a false-negative result or diminished ability to respond to tuberculin. Error in TST administration (subcutaneous injection, insufficient dose) or interpretation of reaction.

There is a very slight risk of having a severe reaction to the tuberculin skin test, especially if you've had tuberculosis (TB). An allergic reaction can cause a lot of swelling and pain at the site. You may have a sore. You cannot get a TB infection from the tuberculin skin test.

A: You can take showers and baths as you normally do. Q: What do I do if my arm itches or blisters? A: Put an ice cube in a washcloth and place it on your arm. DO NOT SCRATCH!

Namely, that if a patient presents for interpretation of the results of a PPD (purified protein derivative of tuberculin) test, it is appropriate to report CPT code 99211. CPT code 86580 is reported for the Mantoux test using the intradermal administration of purified protein derivative (PPD).

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.

An induration of 5 or more millimeters is considered positive in: People with HIV. Recent contacts of people with infectious TB disease. People with chest x-ray findings suggestive of previous TB disease.