PPD is the standard screening test to identify the presence of Mycobacterium tuberculosis infection to aid in the diagnosis of tuberculosis.This test is usually done in people who have been in direct contact with patients infected with the bacteria, even if they show no symptoms of the disease, due to suspected latent TB infection, when the bacteria is installed but has not yet caused the disease.Find out what the symptoms of TUBERCULOSIS are.
The PPD test, also known as a TB skin test or Mantoux reaction, is performed in clinical testing laboratories by a small injection containing proteins derived from bacteria under the skin, and should preferably be evaluated and interpreted by a pneumologist for this purpose.correct diagnosis.
- When PPD is positive.
- There is a good chance of being contaminated with bacteria.
- However.
- Only the PPD test is not enough to confirm or rule out the disease.
- So in case of suspected tuberculosis.
- Your doctor should prescribe other tests.
- Such as chest tests.
- X-rays or bacterial sputum.
- For example.
The PPD test is performed in a clinical laboratory of clinical analysis by injecting a purified protein derivative (PPD), i.e. purified proteins present on the surface of TB bacteria, proteins are purified so that there is no development of the disease in people who do not have it, however, proteins react in infected or vaccinated people.
The substance is applied to the left forearm and the result should be interpreted 72 hours after application, which normally takes the reaction, for example, 3 days after the application of the TB protein, it is recommended to return to the doctor to find the test result, which should also take into account the symptoms presented by the person.
To pass the PPD exam it is not necessary to fast or take other special precautions, it is only recommended to inform the doctor if you are using any type of medication.
This test may be done in children, pregnant women, or people with weakened immune systems, but should not be done in people who may have severe allergic reactions, such as necrosis, ulceration, or severe anaphylactic shock.
The RESULTS of the PPD test depend on the size of the reaction on the skin, as shown in the image and can therefore be:
In some situations, the presence of a skin reaction greater than 5 mm does not mean that the person is infected with the mycobacteria responsible for tuberculosis, for example, people who have already been vaccinated against tuberculosis (BCG vaccine) or who have infection with other types of mycobacteria may have a skin reaction during the test, called a false positive result.
A false negative result, in which the person has infection with the bacteria but does not form a reaction in PPD, can occur in cases of people with weakened immunity, such as people with AIDS, cancer or who use immunosuppressive medications, in addition to malnutrition, over 65 years of age, dehydration or with a serious infection.
Due to the risk of false results, TB should not be diagnosed simply by testing this test, the pneumologist should request additional tests to confirm the diagnosis, such as chest x-ray, immunological tests, and bacilluscopy, which is a laboratory test in which the patient’s sample, usually sputum, is used to detect the disease-causing bacillus.These tests should also be monitored even if PPD is negative, as this test alone cannot be used to rule out diagnosis.