Mantoux Test: Purpose, Procedure, Results, and Limitations

The Mantoux test, also known as the tuberculin skin test (TST), is a widely used diagnostic screening method to detect tuberculosis (TB) infection. It helps identify individuals who may have been exposed to Mycobacterium tuberculosis, the bacterium responsible for causing TB. This test is simple, cost-effective, and commonly used in healthcare settings around the world.

🧪 What is the Mantoux Test?

The Mantoux test involves the intradermal injection of a purified protein derivative (PPD) tuberculin into the skin of the forearm. After 48 to 72 hours, the site of injection is examined for any reaction. A raised, hardened swelling (induration) at the injection site may indicate a TB infection, either latent (inactive) or active.

🎯 Purpose of the Mantoux Test

The primary aim of the Mantoux test is to:

Detect whether a person has been previously exposed to tuberculosis bacteria.
Aid in TB surveillance and control programs.
Screen individuals before employment, immigration, or immunosuppressive therapy.

It is especially used among healthcare workers, students, immigrants from high-TB prevalence countries, and individuals with compromised immune systems.

🩺 Mantoux Test Procedure: Step-by-Step

Injection: A trained healthcare provider injects 0.1 mL of PPD tuberculin intradermally into the inner surface of the forearm.
Waiting Period: The patient must return after 48 to 72 hours to have the site examined.
Assessment: The diameter (in millimeters) of the induration (not redness) is measured using a ruler.

✅ Interpretation of Mantoux Test Results

Positive Result: An induration of a certain size indicates TB infection. The cut-off size for a positive test may vary:
- ≥5 mm: Considered positive in high-risk individuals (e.g., HIV-positive, recent TB contact).
- ≥10 mm: Positive for moderate-risk groups (e.g., healthcare workers, recent immigrants).
- ≥15 mm: Positive in healthy individuals with no known risk factors.

⚠️ A positive test does not confirm active TB disease — it only indicates previous exposure or latent infection.

Negative Result: No significant swelling or a small induration usually means no TB infection. However, false negatives can occur in:
- Recent TB infections (within 8 weeks)
- Immunocompromised individuals
- Infants and elderly patients
- People with certain viral infections or malnutrition

📋 Follow-Up After a Positive Mantoux Test

If the result is positive, further tests are necessary to determine the nature of the infection:

Chest X-ray
Sputum culture or smear
Interferon-Gamma Release Assays (IGRA)

These help differentiate between active TB disease and latent TB infection (LTBI), guiding appropriate treatment.

⚠️ Limitations of the Mantoux Test

Cannot distinguish between latent and active TB
May give false positives in individuals vaccinated with BCG (Bacille Calmette-Guérin)
May give false negatives in immune-suppressed patients or early-stage infection
Needs a follow-up visit, which can be missed

🧾 Summary

The Mantoux Tuberculin Skin Test (TST) is an essential tool for TB screening but not a standalone diagnostic test. A positive result indicates exposure, not disease, and should be followed by additional tests to confirm an active TB infection and begin timely treatment.

🔍 Frequently Asked Questions (FAQs)

Q1. Is the Mantoux test painful?
Only a slight prick is felt during the injection, and most people tolerate it well.

Q2. Can I shower after a Mantoux test?
Yes, you can bathe, but avoid scratching or applying lotions to the injection site.

Q3. What if I miss the 48–72 hour reading window?
The test must be repeated if not read within the proper time frame.

Q4. Does BCG vaccination affect Mantoux results?
Yes, BCG can sometimes cause a false positive, especially in recently vaccinated individuals.