What Is PPD Test or Mantoux Test
Mantoux test or PPD test can show if you have presence of TB infection. The Mantoux test does not differentiate between active TB and latent TB. It only tells presence of tuberculosis bacteria. This TB test is standard method to diagnose latent Tb.
Mantoux Mandel test is also known as Tuberculin Sensitivity Test. In India this test is also often mispronounced as Montu test. If this test for latent Tb is positive doctor may advice another TB test like sputum test to confirm the active TB infection.
Method For Mantoux Test or PPD Skin Test
A standard dose of PPD (Purified protein derivative) tuberculin is injected intradermally in the skin (between the layers of dermis) This intradermal injection is termed the Mantoux technique. A person who has been exposed to the bacteria is expected to show an immune response in the skin. The skin is read for reaction 48 to 72 hours after administration of injection.
Interpretation for PPD Tuberculin Skin Test
The interpretation is based on the sensitivity of skin to injected PPD tuberculin. The reaction is read by measuring the diameter of palpable – raised hardened- area ( induration) area across the forearm. Erythema (redness) is not measured. Just the appearance of raised area does not mean that you have TB. Because different diameters of induration are considered positive in different kind of individuals.
For example. An induration of 5 or more millimeters is considered positive in HIV-infected persons. Induration of more than 10mm is considered positive for children under 4 years of age. So you should depend on your doctor or expert for interpretation.
False Positives to Mantoux test
Some persons may react to the tuberculin skin test even though they are not infected with tuberculosis. The causes of these false-positive reactions may include the following:
• Infection with non-TB Mycobacteria
• Previous BCG vaccination
• Inaccurate Test administration
• Incorrect interpretation
False Negatives to Mantoux test
The reasons for these false-negative reactions may include the following:
• Cutaneous anergy (anergy is the inability to react to skin tests
because of a weakened immune system)
• Recent TB infection (within 8-10 weeks of exposure)
• Very old TB infection (many years old)
• Very young subject (less than 6 months old)
• Recent live virus vaccination (e.g., measles and smallpox)
• Overwhelming TB disease
• Some viral illnesses (e.g., measles and chicken pox)
• Incorrect method of Test administration
• Incorrect interpretation
Side Effects of PPD Skin Test?
Mantoux test does not have any side effects in most individuals. There is very slight risk of reaction like swelling and redness of the arm, this can be controlled by doctor if happens. Allergic reactions are also rare complications.
There is no chance of developing tuberculosis from the PPD test.
What If You Got Positive Skin Test?
If your PPD tuberculin test is positive, do not panic. because
• Active Tb is still not confirmed.
• Latent Tb can be cured easily by taking one medicine for some months.
• If other Tests confirm active TB then it can always be cured in few months.
• Tb diagnosis and treatments are free in India by government, and also easily accessible.
Who Should Get A TB Skin Test
• Those who have had frequent close contact with someone who has active TB disease
• Those living or lived in a country or locality where many people have TB
• Those working or living in a nursing home, clinic, hospital, prison, or homeless shelter, or
• Those who have HIV infection or certain other health problems.
• Consult your doctor about possibility if you have cough for more than 4 weeks.
Please note, doctor may suggest other tests directly like chest X-ray and sputum test without first suggesting Mantoux test. Mantoux tells about presence of tuberculosis bacteria in latent state or active state. Other tests may confirm the active Mycobacterium TB infection.