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Two-Step Tuberculosis (TB) Skin Test

Tuberculosis is considered one of the world’s leading infectious-disease killers, and can be highly infectious and very easily spread.  A simple test can be used that uses the body’s natural reaction against a foreign substance to measure or look for the possibility of a current infection with tuberculosis.

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Test Details

A small amount of a purified protein based testing liquid (tuberculin) is injected under the skin.  The body’s reaction, or lack of reaction, is then measured or observed after a set amount of time to determine if there is potentially an active infection.

This test is commonly used for screening in a variety of settings, including: employment, immigration, education, etc.

Some healthcare centers, schools or workplaces will require TWO separate but consecutive skin tests.  This is sometimes called a TWO-STEP TB Test.  The second skin test is placed at least 7 days, but no more than 27 days, after the reading/interpretation of the first test.  Both tests must be placed and read within 28 days total in order to consider the two-step test complete.

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FAQs

WHY DO I NEED THIS TEST?

While tuberculosis is highly infectious, it is fortunately also very easily preventable and treatable.  Breathing in the bacteria that causes the disease does not automatically lead to an active infection.  Instead, most healthy immune systems can fight the bacteria and prevent it from growing too much.  This leads to what is called a “latent infection”, which is simply another term for an infection that is not active but could still become active later.  Most people with latent TB will not have symptoms or feel sick; but treatment should still be provided to prevent these people from ever developing active TB.

WHY DO I HAVE TO RETURN IN 2-3 DAYS?

Since the skin test relies on the body’s natural reaction against the testing fluid (tuberculin), you will have to wait an appropriate amount of time for that reaction.  Less than 48 hours is not enough time for a reaction to form, and anything more than 72 hours could mean a false negative result.

WHAT HAPPENS IF I MISS MY RETURN TIME WINDOW?

If your skin test cannot be read or interpreted properly within the 48-72 hours of placement, you will either need another skin test to be placed, which means you will need to return for a third time for a proper read within the required 48-72 hours.

WHY ARE THERE TWO TESTS?

The two-step test is typically required for people who will have periodical or regular skin tests, such as healthcare workers, or anyone else in a high-risk situation for exposure to TB.

AM I REQUIRED TO FAST?

No fasting or any other preparation is needed for the test.

WHAT IF I WAS VACCINATED WITH THE BCG (TB Vaccine) AS A CHILD?

While this vaccine is not commonly used in the US, it is highly common outside of the US.  Those who were born outside of the US very likely could have received this vaccine as an infant or child.  In some people who received the BCG, skin tests can potentially cause a positive reaction, even though the same person does not necessarily have latent TB.  If you were vaccinated, and/or you have had a positive skin test in the past, please speak with your healthcare provider or physician before receiving a skin test for TB.  It is possible that a blood test might be preferred.

IS A DOCTOR’S ORDER REQUIRED?

We provide the doctors’ orders to get lab testing done at Any Lab Test Now.

IF I HAVE QUESTIONS ABOUT MY TESTS RESULTS WHO SHOULD I CONTACT?

We recommend you share your results with your physician, especially if there is a possible positive reaction. Additional tests and treatment will be at the guidance of your physician.