How to Tell If Your TB Skin Test Is Positive?
A hard, red bump means your TB skin test is positive. Your doctor will measure how hard the bump is (induration). They’ll consider your risk factors to decide if your test is positive.
To be positive, your bump must be:
- More than or equal to 5 mm, if your immune system is weak.
- 10 mm, if you’re a healthcare worker.
- 15 mm, for everyone else.
It’s important to see your doctor for a follow-up appointment to get a second opinion, even if you think you know the outcome of your test based on the look of your skin 48 to 72 hours after the initial liquid injection.
What Happens During a TB Test?
A TB skin test, commonly known as a Mantoux tuberculin skin test (TST), is often well tolerated and rarely results in side effects. There are two components to the test:
Section One
A physician injects a small quantity of tuberculin beneath the skin. A sterile extract of a pure protein derivative (PPD) derived from the TB-causing bacterium is called tuberculin. The injection site will develop a little whitish bump.
Section Two
Your doctor will examine your skin 48 to 72 hours after the injection to see how the tuberculin affected it. The way your skin reacts can help the doctor diagnose you with tuberculosis. If you wait more than 72 hours for a doctor to examine your skin, you must start a new test.
What Happens If Your TB Skin Test is Positive?
If your TB test is positive, you have symptoms, or you’re at high risk of TB exposure, your doctor will likely prescribe medicine to kill the infection and reduce symptoms.
If you have a positive test but are at low risk, your doctor might suggest a TB blood test to confirm the diagnosis. While the blood test is more accurate than the skin test, it can’t tell the difference between a latent TB infection and active TB disease.
Summing Up!
A positive TB skin test suggests that you could have had an infection with the TB-causing bacterium. It does not, however, imply that you now have active tuberculosis. More testing is required to find out if you have an active infection, such as a blood test or a chest X-ray.
At Bharmal Internal Medicine, our experts perform TB skin tests. We’ll help you stay healthy. Call us at (817) 784-0052 to schedule your TB Skin Test.