Tuberculosis skin test

Overview

The tuberculosis (TB) skin test is a simple test that shows whether you have been infected with the bacteria that cause TB. It is also called the Mantoux test. A small amount of fluid (tuberculin) is injected just under the skin of your arm. After 48 to 72 hours, a healthcare professional checks the spot for swelling or redness. A reaction may mean you have a TB infection, but it does not tell if the infection is active (making you sick) or inactive (latent).

The TB skin test is commonly used in many countries, especially for screening people who may have been exposed to TB, such as healthcare workers, close contacts of someone with active TB, or people moving from areas where TB is more common.

The test is used for people of all ages, but it is most often given to adults and children who have a higher risk of TB infection. People with weakened immune systems (for example, from HIV, cancer treatment, or certain medicines) may also be tested.

Symptoms

Causes

Main causes

• The TB skin test is used to detect infection with the bacterium Mycobacterium tuberculosis.
• TB bacteria spread through the air when someone with active TB coughs, sneezes, or talks.

Risk factors

• Living or working in close contact with someone who has active TB.
• Having a weakened immune system (for example, from HIV, organ transplant, or long-term steroid use).
• Being from or traveling to areas where TB is common, such as parts of Africa, Asia, or Eastern Europe.

When to see a doctor

See a doctor urgently if:

• If you have symptoms of active TB (persistent cough, coughing up blood, fever, night sweats, weight loss) you should see a doctor the same day.
• If you have been in close contact with someone known to have active TB, you should be tested as soon as possible.

Book a routine appointment if:

• If you are in a higher-risk group (healthcare worker, recent travel to high-risk area, weakened immune system), ask your doctor about routine TB screening.
• If you have a positive TB skin test, you will need a follow-up appointment for further tests (like a chest X-ray and possibly a sputum sample).

Diagnosis

The TB skin test is a diagnostic tool for infection, not a diagnosis of active TB. If the skin test is positive, further tests are needed to find out if the infection is active or latent.

Tests that may be done

• TB skin test (Mantoux test) – injection of tuberculin fluid under the skin.
• Chest X-ray – to see if there are changes in the lungs that suggest active TB.
• Sputum test – a sample of phlegm (mucus from the lungs) is sent to a lab to look for TB bacteria.
• Blood tests (IGRA) – sometimes used instead of the skin test, especially if BCG vaccine was given.

What to expect at your appointment

The test is done in a doctor’s office or clinic. A small needle is used to inject a tiny amount of fluid just under the skin of your forearm. This feels like a quick pinch. You must return within 48 to 72 hours to have the spot measured. The doctor or nurse will feel for a raised area (induration) and measure it with a ruler. You may also be asked about your medical history and any symptoms you have.

Treatment

If the TB skin test is positive, treatment depends on whether the infection is active or latent. Latent TB infection is treated to prevent it from becoming active in the future. Active TB disease always requires treatment with a combination of several antibiotics taken over several months.

Self-care at home

• During treatment for TB, it is important to take all medicines exactly as prescribed and finish the full course.
• Get plenty of rest and eat a nutritious diet to support your immune system.
• If you have active TB, you may need to stay home from work or school until you are no longer contagious (usually after two weeks of treatment).

Medical treatments

Treatment for TB infection involves taking a course of antibiotics. The specific medicines and how long you take them depend on whether you have latent or active TB, your age, and your overall health. Your doctor will prescribe a regimen that may last from several months to a year. It is vital to complete the entire course, even if you start feeling better, to prevent the bacteria from becoming resistant.

When is surgery considered?

Surgery is rarely needed for TB. In some cases when drug-resistant TB causes severe damage to lung tissue, surgery may be considered to remove infected parts of the lung.

Living with this condition

If you have latent TB infection, you can live normally. You are not contagious and do not need to isolate. You may need to take medication for several months to prevent the infection from becoming active. If you have active TB, you will need to take medications daily and may need to avoid close contact with others for the first few weeks of treatment.

Lifestyle tips

• Take your TB medications exactly as prescribed, at the same time each day.
• Attend all follow-up appointments and tests as recommended by your healthcare team.
• Avoid smoking and excessive alcohol, which can weaken your lungs and immune system.

Diet and exercise

A balanced diet rich in fruits, vegetables, whole grains, and lean protein helps support your immune system. Stay active with gentle exercise like walking, but get adequate rest, especially during active TB treatment.

Mental health and emotional wellbeing

Being diagnosed with TB infection or disease can cause anxiety, fear, or sadness, especially because treatment may take months. It is okay to reach out for emotional support. Talk to your doctor about counselling or support groups. If you have thoughts of harming yourself, call your local emergency number immediately.

Prevention

TB infection can often be prevented by avoiding close, prolonged contact with people who have active TB, especially in enclosed spaces. Good ventilation helps reduce the spread of TB bacteria. If you have latent TB, treatment can prevent it from becoming active.

Vaccines

A vaccine called BCG (Bacille Calmette-Guérin) is used in some countries to prevent severe forms of TB in children. However, BCG vaccination can cause a false positive TB skin test, which is why the skin test is often replaced by a blood test (IGRA) in people who have had the BCG vaccine.

Screening programmes

Screening with the TB skin test or blood test is recommended for people at higher risk, such as close contacts of someone with active TB, people with HIV, healthcare workers, and new arrivals from areas with high TB rates.

Complications

If left untreated

• If untreated, latent TB infection can develop into active TB disease, which can damage the lungs and spread to other organs.
• Active TB can cause severe illness, permanent lung damage, and even death if not treated properly.
• Without treatment, a person with active TB can spread the infection to others.

Long-term outlook

The outlook for TB infection is excellent with proper treatment. Latent TB can be cured, and active TB is almost always curable with a full course of antibiotics. The key is to follow your doctor’s advice, take all medications as prescribed, and attend follow-up appointments. With timely treatment, most people recover completely and return to their normal lives.

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