how to know if your tb test is positive

3 min read 18-12-2024

Tuberculosis (TB) is a serious bacterial infection that primarily affects the lungs. A TB skin test, also known as a Mantoux tuberculin skin test (TST), is a common way to screen for infection. Understanding how to interpret your test results is crucial. This article will guide you through recognizing a positive TB test. Remember, a positive test doesn't automatically mean you have active TB disease. Further testing is always necessary.

Understanding the TB Skin Test

The TB skin test involves a small injection of tuberculin under your skin. You'll return 48-72 hours later for a reading. A healthcare professional will measure the area of induration (hardened, raised area) at the injection site. The size of this area determines whether the test is considered positive or negative.

What Does a Positive TB Test Mean?

A positive TB test indicates you've been exposed to the bacteria that causes TB. This exposure could have happened at any point in your life. It doesn't necessarily mean you have active TB disease, which is contagious. A positive result means you have latent TB infection (LTBI). LTBI means the bacteria is present in your body but isn't actively causing illness. However, it can develop into active TB later on.

How to Interpret Your TB Test Results

The interpretation of a TB skin test varies depending on factors such as your risk factors, your immune status, and where you live. Your doctor will consider these factors when interpreting your results. General guidelines are:

Positive: The size of the induration is generally 5 mm or more in individuals with high-risk factors (like HIV infection, recent contact with a person with active TB, organ transplant recipients, or those with certain immune disorders). For individuals with low risk factors, the size needs to be 10mm or more. A reaction of 15mm or greater is usually considered positive in most people.
Negative: The induration is less than the size mentioned above depending on your risk factors.
Indeterminate: Sometimes the result is unclear, often due to improper test administration. If this happens, your doctor will advise you on the next steps.

What to Do if Your TB Test is Positive

A positive TB test result requires further evaluation. Your doctor will likely recommend:

Chest X-ray: This helps to visualize your lungs and detect any abnormalities.
Sputum Culture: If a chest X-ray shows abnormalities, a sputum (lung mucus) culture may be necessary to confirm the presence of active TB bacteria.
Treatment: If active TB is confirmed, you'll need treatment with antibiotics. LTBI, on the other hand, often requires preventative treatment to prevent it from developing into active TB.

It's critical to follow up with your doctor if your TB test is positive. They can determine if you have latent or active TB and recommend the appropriate course of action.

Other TB Tests

Besides the skin test, other tests can detect TB infection or disease:

Interferon-gamma release assays (IGRAs): These blood tests detect an immune response to TB bacteria. They are useful alternatives to the skin test.
Chest X-ray: As mentioned before, this imaging test can reveal signs of active TB in the lungs.
Sputum tests: These laboratory tests analyze sputum samples to identify the presence of TB bacteria.

Frequently Asked Questions (FAQs)

Q: Can a TB skin test be wrong?

A: While the TB skin test is generally reliable, it can yield false-positive or false-negative results. Factors such as previous BCG vaccination (a TB vaccine), other infections, or weakened immune systems can affect the accuracy.

Q: How long does it take to get TB test results?

A: The skin test results are available within 48-72 hours after the injection. Other tests, such as blood tests, chest X-rays, and sputum cultures, may take longer.

Q: What are the symptoms of active TB?

A: Symptoms of active TB can include a persistent cough, fever, night sweats, weight loss, chest pain, and fatigue. However, some individuals may have no symptoms.

This information is for educational purposes only and shouldn't be considered medical advice. Always consult a healthcare professional for diagnosis and treatment of any medical condition, including tuberculosis. A proper medical evaluation is crucial to determine the appropriate course of action following a positive TB test. Remember to always follow your doctor's recommendations.