What is a TB test, and how is it used to diagnose tuberculosis?

Question

I recently had a TB test as part of a routine check-up, but I don’t fully understand what it measures or why it’s necessary. I know it checks for tuberculosis, but how does the test work and what does it tell the doctor about my health?

What is a TB test, and how does it detect tuberculosis infections? I read that it can either be a skin test or a blood test—what is the difference between them, and which one is more accurate? Also, how does the TB test work to determine whether someone has been exposed to the bacteria or if they currently have an active infection?

I also want to know what happens if a TB test comes back positive. Does that always mean active tuberculosis, or can there be false positives from previous exposure or vaccinations? How is TB treated, and is early detection important for preventing the spread of the disease?

If anyone has had a TB test, what was the process like, and what did the results mean for your health? Did it lead to further testing or treatment?

Dr Sujal Patil · Accepted Answer

A TB test is used to detect tuberculosis (TB), a bacterial infection caused by Mycobacterium tuberculosis. There are two main types of TB tests:

1. TB Skin Test (Mantoux Test):
A small amount of tuberculin is injected just under the skin of the forearm.
After 48-72 hours, a healthcare provider checks the injection site for swelling.
Interpretation: A raised bump may indicate TB exposure. However, this test cannot distinguish between latent TB (inactive) and active TB. Prior BCG vaccination or other infections can cause false positives.
2. TB Blood Test (IGRA - Interferon Gamma Release Assay):
Measures how the immune system reacts to TB bacteria in the blood.
It’s more specific and less likely to give false positives from prior vaccinations.
Preferred for: Those with prior BCG vaccination or those who may not return for skin test readings.
Positive TB Test:
A positive result doesn’t necessarily mean active TB. It could indicate:

Latent TB: The bacteria are present but inactive, and there are no symptoms.
Active TB: Symptoms like cough, fever, and weight loss are present. Further tests (e.g., chest X-ray, sputum test) are needed to confirm active disease.
Treatment:
Latent TB: Preventive antibiotics may be prescribed to avoid progression to active TB.
Active TB: A combination of antibiotics is taken for several months to fully eradicate the infection.
Importance of Early Detection:
Early identification helps prevent TB from progressing or spreading to others. If your test is positive, your doctor will guide you on next steps to ensure proper treatment or monitoring.

If you’ve had a TB test, it’s important to discuss the results with your doctor to fully understand their significance and any further steps.

What is a TB test, and how is it used to diagnose tuberculosis? - #14774

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