What You Should Know About Positive TB Test Reactions

May 30, 2025
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Tuberculosis (TB) is a global health concern. Although it is a treatable disease, it can easily spread if not detected early. One of the most common ways of detecting TB is through a skin test, also known as the Mantoux test. If you or someone you know is about to take this test, then you might wonder what the positive results will look like.

In this blog, we will learn what you can interpret from the results of the TB skin test. From understanding the test to the signs of a positive test, this guide will make the entire process easy for you.

What Is a TB Skin Test?

A TB skin test is a diagnostic process that helps you know whether you have been exposed to the bacteria or not. During this test, you are injected with a small amount of protein derivative. The next 48-72 hours are strictly monitored to see the body’s reaction to the substance. If your immune system recognizes the substance as a threat, then you will get a skin reaction.

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Timeframe for Results

The results are ready in the next 48-72 hours after the injection is given. The time in between is critical as the body’s immune system starts to respond. A professional will examine the injected area for any swelling. Remember that reading the results too late or too early will lead to inaccurate readings. So, taking the results between the given timeframe is crucial for accurate results.

What Does a Positive Result Look Like?

A positive TB skin test is indicated by a firm bump at the injected site. The size of the bump is the main indicator, not the redness around it. A healthcare provider will measure the bump using a ruler across your forearm, in millimeters.

Measurement

To see if the reaction is positive, the expert will measure the area for hardness across your forearm. When the bump exceeds a specific size, the test results are positive for TB.

5mm or More

People with high risk are the ones who are HIV positive or have had an organ transplant surgery. Having a bump that exceeds 5mm is extremely risky.

10mm or More

When your results show a bump of about 10mm and you are an immigrant or someone battling a health condition already, then your TB results may come back positive.

15mm or More

Even if you do not have any underlying health conditions, or even if you are not an immigrant, having a bump of more than 15mm can cause you to test positive for TB.

What to Do After a Positive TB Skin Test?

If you test positive for TB, it does not mean you have it actively. It means the bacteria have entered your body and need urgent treatment.

Immediately schedule a chest X-ray to check for any signs of active TB.
You need to undergo a physical exam and have a healthcare professional review your case.
If recommended, you need to take the Interferon-Gamma Release Assay (IGRA) blood test.
Keep your doctor informed about all the treatments and vaccinations you have received previously.
Until the active TB is ruled out, follow your prescribed treatment.
Isolate yourself and follow safety guidelines to prevent spreading it to others.

Final Thoughts

A positive TB skin test can be alarming. However, it is important to get urgent care once the results come back positive. Understanding TB and knowing what a positive test will look like can help you take care of your health.

At Bharmal Internal Medicine, our healthcare experts will start your treatment right away. This is to prevent the TB from spreading. So, schedule your screening today with our experts by calling us at (817) 784-0052.