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how does tb test positive look like

how does tb test positive look like

3 min read 30-12-2024
how does tb test positive look like

Tuberculosis (TB) testing helps determine if you've been infected with the bacteria that cause the disease. Several types of tests exist, and a positive result doesn't automatically mean you have active TB. Understanding what a positive result looks like for each test is crucial.

Types of TB Tests and Their Positive Results

Several tests can detect TB infection. Here's a breakdown of what a positive result looks like for each:

1. Tuberculin Skin Test (TST) or Mantoux Test

  • The Test: A small amount of tuberculin (a protein from the TB bacteria) is injected under the skin of your forearm. You return 48-72 hours later for a reading.

  • Positive Result: A positive result is indicated by a raised, hardened area (induration) at the injection site. The size of the induration determines the positivity, and this varies based on risk factors (e.g., age, immune status, recent contact with someone with TB). A healthcare professional measures the induration in millimeters. A larger induration generally suggests a higher likelihood of infection. It's not the redness (erythema) but the hardness (induration) that matters. The size threshold for a positive test changes depending on your risk factors—your doctor will interpret the result.

2. Interferon-Gamma Release Assays (IGRAs) – Blood Tests

  • The Test: A blood sample is taken and tested for your immune system's response to TB bacteria. Two common IGRAs are QuantiFERON-TB Gold and T-SPOT.TB.

  • Positive Result: A positive result shows that your immune system has reacted to the TB antigens in the blood test. The lab will provide a numerical result, indicating the level of response. A result exceeding a certain threshold is considered positive. Your healthcare provider will explain what the numbers mean and whether further testing is needed.

3. Chest X-Ray

A chest X-ray isn't a direct TB test; it's used to detect active TB disease, not just infection.

  • Positive Result: A chest X-ray might show abnormalities consistent with active TB, such as:
    • Infiltrates: White patches or shadows in the lungs.
    • Cavities: Holes in the lung tissue.
    • Nodules: Small, rounded lumps in the lungs.
    • Lymph node enlargement: Swollen lymph nodes near the lungs.

A positive chest x-ray requires further investigation, usually with sputum tests to confirm the presence of the TB bacteria.

What to Do if Your TB Test is Positive

A positive TB test result doesn't automatically mean you have active TB disease. It indicates that you've been infected with the bacteria at some point. Your doctor will need to conduct further investigations to determine if you have latent TB infection (LTBI) or active TB disease.

Latent TB infection (LTBI): This means the TB bacteria are present in your body, but they are not actively causing disease. You are not contagious and usually don't need treatment unless your immune system is weakened.

Active TB disease: This means the TB bacteria are actively multiplying and causing disease. You are contagious and require treatment with antibiotics.

Further testing may involve:

  • Sputum tests: Samples of your phlegm are examined for the presence of TB bacteria.
  • Additional chest x-rays: To monitor the progression of any lung abnormalities.
  • CT scan: To get a more detailed image of the lungs.

Your doctor will discuss the results of these tests and recommend the best course of action based on your individual circumstances. It's crucial to follow your doctor's recommendations for treatment and follow-up care.

Conclusion

A positive TB test doesn't automatically equal active TB. Understanding what a positive test looks like for each type of test and knowing when further investigation is needed is essential. If you have concerns or questions about your TB test results, consult with your healthcare provider. They can provide personalized guidance and support.

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