Mantoux Test

The Mantoux test, also known as the tuberculin skin test (TST), is a diagnostic tool used to assess if a person has been infected with Mycobacterium tuberculosis, the bacteria that causes tuberculosis (TB).

Procedure

The Mantoux test involves injecting a small amount of purified protein derivative (PPD) tuberculin into the skin of the forearm. The injection is typically given just beneath the surface of the skin, and a small bump or wheal forms at the site of the injection.

Interpretation

The test is read 48 to 72 hours after the injection by measuring the diameter of induration (swelling) across the forearm. The results are interpreted as follows:

• 0-4 mm: Negative result, indicating no infection or a very low risk of TB.
• 5-9 mm: Doubtful result, may require repeat testing or further evaluation.
• 10 mm or more: Positive result, indicating likely TB infection. Further testing, such as chest X-rays and sputum tests, is typically required to confirm the diagnosis.

Indications

The Mantoux test is commonly used in the following situations:

• Screening for latent TB infection in high-risk individuals, such as healthcare workers or those with weakened immune systems.
• Diagnosing active TB disease in patients with symptoms such as cough, fever, and weight loss.
• Monitoring the effectiveness of TB treatment.

Contraindications

The Mantoux test is contraindicated in individuals with:

• Severe skin conditions, such as eczema or psoriasis, that may interfere with the test results.
• Previous severe reactions to tuberculin injections.

Side Effects

Common side effects of the Mantoux test include:

• Mild redness and swelling at the injection site.
• Itching or burning sensations.

Limits of the Test

The Mantoux test has some limitations, including:

• False-negative results can occur in individuals with weakened immune systems or those who have received the BCG vaccine.
• False-positive results can occur due to cross-reactivity with other mycobacteria.