Tuberculin Test (TT) Test
Tuberculin Test (TT) Test
The Tuberculin Test (TT), also known as the Mantoux Tuberculin Skin Test (TST), is a diagnostic tool used to detect latent or active tuberculosis (TB) infection. It involves injecting a small amount of purified protein derivative (PPD) tuberculin under the skin and measuring the immune response after 48 to 72 hours. The test helps identify individuals who have been exposed to Mycobacterium tuberculosis, the bacterium responsible for tuberculosis.
The tuberculin test is commonly used for screening high-risk individuals, including healthcare workers, immunocompromised patients, and those in close contact with TB-infected individuals. A positive reaction does not confirm active TB but indicates prior exposure or infection, necessitating further evaluation.
What is the Tuberculin Test Used For?
- Detecting latent TB infection (LTBI) in asymptomatic individuals.
- Identifying individuals at high risk of developing active TB, such as immunocompromised patients.
- Screening healthcare workers, travelers, and people in high TB prevalence areas.
- Assessing TB exposure in contacts of confirmed TB patients.
Aiding in TB diagnosis when combined with clinical and laboratory findings.
Symptoms of Tuberculosis
Some of the symptoms of an active infection of tuberculosis are
Cough lasting more than two – three weeks with or without blood
Fever and Night Sweats
Fatigue
Appetite loss
Unexplained weight loss
Pain in different parts of the body
Swollen glands
Procedure for the Test
A 0.1 mL injection of PPD tuberculin is administered intradermally on the forearm. The site is marked, and no bandage is applied. The reaction is evaluated 48 to 72 hours later by measuring the induration (raised, hardened area) in millimeters. Erythema (redness) alone is not considered a positive reaction.
Interpretation of Test Results
A positive result indicates TB exposure but does not confirm active disease; additional tests such as chest X-ray, sputum analysis, or IGRA (Interferon-Gamma Release Assay) may be required.
|
Induration Size |
Interpretation |
|
≥ 5 mm |
Positive in HIV-positive individuals, recent TB contacts, organ transplant recipients. |
|
≥ 10 mm |
Positive in healthcare workers, recent immigrants, people with high-risk conditions. |
|
≥ 15 mm |
Positive in individuals with no known risk factors for TB. |
|
0–4 mm |
Negative result; unlikely TB infection, but further testing may be needed if symptoms are present. |
FAQs
Can a prior BCG vaccine cause a false-positive result?
Yes, BCG vaccination can cause a mild positive reaction, but it does not necessarily indicate TB infection.
How soon after TB exposure should I get tested?
Testing is recommended 2 to 10 weeks after exposure to ensure an accurate immune response.
What if my test is positive but I have no symptoms?
You may have latent TB infection (LTBI), which requires further evaluation and possible preventive treatment.
Can I take the test if I have a skin condition?
Yes, but inform your healthcare provider, as skin conditions or allergies may affect the reaction site.
What follow-up tests are needed for a positive result?
- Chest X-ray, sputum culture, and IGRA blood test may be recommended for further assessment.
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