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Positive TB Skin Test vs. Negative TB Skin Test: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on February 12, 2024
A Positive TB Skin Test indicates a likely exposure to tuberculosis bacteria, while a Negative TB Skin Test suggests no evidence of exposure.

Key Differences

A Positive TB Skin Test, typically indicated by a raised, red bump at the test site, suggests that the individual has been exposed to the tuberculosis bacteria. In contrast, a Negative TB Skin Test, where no significant reaction occurs at the test site, implies a lack of TB exposure.
The Positive TB Skin Test does not necessarily mean active tuberculosis; it could indicate a latent or past infection. On the other hand, a Negative TB Skin Test generally means the person does not have a latent or active TB infection.
Certain conditions, like a weakened immune system, can lead to a false-negative result in a TB Skin Test, while a positive result might require further testing to confirm active TB. Negative TB Skin Tests are usually more straightforward, indicating no TB infection.
Vaccination with the Bacille Calmette-Guérin (BCG) vaccine can cause a false-positive TB Skin Test, whereas a Negative TB Skin Test is unaffected by this vaccine.
A Positive TB Skin Test requires careful evaluation and possibly additional tests, while a Negative TB Skin Test is typically conclusive in indicating no TB infection.

Comparison Chart


Suggests exposure to TB bacteria.
Suggests no exposure to TB bacteria.

Physical Reaction

Raised, red bump at the test site.
No significant reaction at the test site.

Implication for Active TB

Does not confirm active TB, further testing needed.
Generally rules out active TB.

Effect of BCG Vaccination

Can cause a false-positive result.
Unaffected by BCG vaccination.

Need for Additional Testing

Often requires further tests to confirm or rule out active TB.
Usually no additional testing required unless circumstances change.

Positive TB Skin Test and Negative TB Skin Test Definitions

Positive TB Skin Test

Indicates likely exposure to TB bacteria.
Her Positive TB Skin Test led to further diagnostic procedures.

Negative TB Skin Test

Indicates no detectable TB exposure.
Her Negative TB Skin Test was a relief, showing no signs of TB.

Positive TB Skin Test

Requires further evaluation to confirm active TB.
Following his Positive TB Skin Test, he underwent a chest X-ray.

Negative TB Skin Test

Typically does not require further TB testing.
With a Negative TB Skin Test, no additional TB screening was necessary.

Positive TB Skin Test

Might be influenced by prior BCG vaccination.
Her Positive TB Skin Test was attributed to her BCG vaccination as a child.

Negative TB Skin Test

Unaffected by previous BCG vaccination.
Despite his BCG vaccination, his TB Skin Test was Negative.

Positive TB Skin Test

Can result from a latent or previously treated TB infection.
Despite feeling healthy, his Positive TB Skin Test revealed a past infection.

Negative TB Skin Test

Shows no immune response to the tuberculin skin test.
The absence of a reaction on his arm confirmed a Negative TB Skin Test.

Positive TB Skin Test

Shows an immune response to tuberculin used in the test.
The test's raised bump was a classic sign of a Positive TB Skin Test.

Negative TB Skin Test

Generally rules out current or past TB infection.
The Negative TB Skin Test suggested she had never been exposed to TB.


Can BCG vaccination affect a TB Skin Test result?

Yes, it can cause a false-positive result.

Can someone with a Negative TB Skin Test have TB?

It's rare, but possible in cases of weakened immunity.

Does a Negative TB Skin Test need follow-up?

Not usually, unless there are symptoms or risk factors for TB.

Is a Negative TB Skin Test conclusive?

Generally, it rules out TB infection unless there's a risk of false negatives.

What does a Positive TB Skin Test indicate?

It suggests exposure to tuberculosis bacteria.

Can a Positive TB Skin Test mean active TB?

Not necessarily; it could indicate latent or past infection.

What does a Negative TB Skin Test mean?

It suggests no exposure to TB bacteria.

Are further tests needed after a Positive TB Skin Test?

Yes, to determine if it's an active TB infection.

Is a Positive TB Skin Test always accurate?

No, it can be influenced by factors like past vaccinations.

Are there false negatives in TB Skin Tests?

Yes, especially in individuals with compromised immune systems.

How long after exposure does a TB Skin Test become positive?

Typically, 2-10 weeks after exposure to TB bacteria.

Can a Positive TB Skin Test indicate immunity to TB?

No, it indicates exposure, not immunity.

Is it safe for pregnant women to have a TB Skin Test?

Yes, TB Skin Tests are considered safe during pregnancy.

How is a Positive TB Skin Test confirmed?

Through additional tests like chest X-rays or sputum tests.

How is a TB Skin Test performed?

By injecting a small amount of tuberculin under the skin.

Can a Negative TB Skin Test turn positive later?

Yes, if exposed to TB after the initial test.

What factors can lead to a false Positive TB Skin Test?

Previous TB infection, BCG vaccination, or non-TB mycobacteria exposure.

How common are Positive TB Skin Tests in TB-endemic areas?

Quite common due to higher exposure rates.

Can someone with a latent TB infection have a Positive TB Skin Test?

Yes, latent TB often results in a positive test.

What is the treatment for a Positive TB Skin Test?

Treatment depends on whether it's latent or active TB.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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