Tuberculin-Mantoux test or IGRA for the diagnosis of tuberculosis. These are the screening tests to reach a diagnosis of latent or active tuberculosis.
INFORMATION
Il “tuberculin test” It is also known as “Purified Protein Derivative PPD” or “Mantoux Test” or “Latent Tuberculosis Infection Test TST” it is also referred to as TB Screening Test.
WHERE TO DO THE TST TEST OR MANTOUX TEST
If you need a test for TB, namely MANTOUX or the QUANTIFERON test or IGRA test pYou can take the TST or Mantoux test at the medical center specialized in infectious and tropical diseases Cesmet-Clinica del Viaggiatore. The reports and certifications attesting the test result are therefore officially recognized for competitions, university institutions and other official requests. You can Request information or book by clicking here e leaving your details, specifying the reason for requesting the test or you can write to seg.cesmet@gmail.
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WHY AND WHEN TO TAKE THE TEST
If you want to exclude or verify the presence of Mycobacterium tuberculosis in your body, it is necessary to carry out the screening test for active or latent TB.
The screening test is required to demonstrate negativity to the bacterium in case of public competitions; enrollment in medical and biological sciences faculties; work in environments with vulnerable or at-risk people. It is also useful before and after international travel in environments and countries considered at risk of Tuberculosis.
Screening testing is indicated in case of exposure to TB; in case of specific symptoms or in the presence of risk factors for active TB.
It is therefore useful for people at risk of developing tuberculosis due to their health situation or who are at risk in the event of contact with the bacterium.
Among these people:
• those with a compromised immune system, such as those who are positive or have full-blown AIDS, who are therefore more susceptible to TB;
• who is found in housing conditions deemed to be at risk, such as those living in homeless shelters, refugee camps, nursing homes, schools and penitentiary institutions;
• those who show suspicious symptoms of TB;
• those who come from or have lived for a certain period in countries where TB is endemic;
• those who use injection drugs;
HOW TO TAKE THE TEST
For the tuberculin skin test, a minimal quantity of a derivative is injected into the volar part of the forearm (flexor part).
purified protein (PPD) in solution (1 ml). This is injected subcutaneously and does not require any special preparation.
CHARACTERISTICS OF THE EXAM
The tuberculin skin test, also called the “Mantoux test”, highlights and demonstrates the presence of M.Tuberculosis in the body, but does not discriminate between active disease and latent form.
To make a definitive diagnosis of “active tuberculosis,” in addition to a positive test result, a clinical evaluation based on specific symptoms is required, and additional diagnostic tests such as Mycobacterium culture and serial x-rays are required.
MICROBIOLOGICAL CHARACTERISTICS
Mycobacterium tuberculosis that comes into contact with the organism, particularly with the respiratory mucosa, can cause an inactive (latent) infection by remaining silently within the infected lymphocytes; or it can cause an active and progressive infection with the Mycobacterium actively reproducing intracellularly.
The cellular immune response of about 90% of people infected with Mycobacterium controls bacterial growth and reproduction within the body and limits the infection to a few lymphocyte cells. The bacteria are sequestered and inactivated in these cells but remain viable. Therefore, infected people do not show symptoms of the disease even though they are carriers of a latent infection.
Latent and asymptomatic infection can last for years, from the first contact, without manifesting itself. In case of lowered defenses or poor functioning
immune system function, immunodeficiency, Mycobacterium can resume its growth with the resumption of active disease and growth and invasion of bacteria within the histiocytic system (lymph nodes – lymphocytes – lymphatic system).
“Active TB” causes discomfort and vague or obvious symptoms in the patient. In case of activation and revitalization of the bacteria, TB can be transmitted through respiratory secretions, sputum, aerosol released by coughing, sneezing, talking or breathing.
March 24, 2023: World Tuberculosis Day to find out more click herei
To learn more about TBC click here.
Institutional and international references: WHO; Ministry of health; ISS;
If there is a risk that the first skin test will give a false negative reaction, a second skin test can be performed which will further stimulate the immune system and thus provide a positive result.
The tuberculin skin test should not be repeated if a person has already had a positive result for the test. Once a positive result is found, the test will always give the same result but the skin reaction to the tuberculin may become more aggressive.
METHOD OF PERFORMING THE TEST
No venous blood is drawn, but one ml of solution containing a purified protein derivative (PPD) of the M. tuberculosis antigen is injected. The forearm is disinfected with alcohol and a small amount of PPD is injected subcutaneously with a 1 ml insulin syringe (fine needle). The injected liquid forms a bubble at the injection site. It is advisable to leave the injection site uncovered, without wetting or soaping it for 48 or 72 hours. Then a skin reaction will be verified.
The skin test, even if negative, may cause slight discomfort or pain at the injection site.
The live, perhaps attenuated, bacteria is not injected under the skin. The tuberculin skin test or Mantoux test measures the immune system's response to an antigen/protein derived from the bacteria through a superficial skin reaction.
TEST RESULTS
The infection caused develops a "skin reaction" characterized by a red and swollen bump of different sizes and with different degrees of discomfort, itching or pain. The reaction is given by the sensitivity of the system to the action of the tubercular protein. The reaction of the sensitized lymphocyte cells, in the presence of bacteria, causes the activation of the inflammatory response, with production of histamine, activation of the complement cascade and release of a series of cytokines that cause the tubercular reaction. The absence of response demonstrates the absence of Mycobacterium from the organism.
To interpret the tuberculin skin test, it is necessary to evaluate the inflammatory reaction in the injection area after 48/72 hours. In the case where there is a more or less evident inflammatory reaction (positive test), the size of the red wheal, evidence of the inflammatory reaction, is evaluated at the injection site, whose size (diameter) quantifies the response and therefore the contact with the tuberculosis mycobacterium. The size of the wheal, the sensitivity to inflammation and the characteristic of the lesion determined by the injected protein, varies based on the state of presence of the bacterium, the state of health and the age of the subject on whom the test is performed.
It should be noted that, despite an ongoing tuberculosis infection, in children, the elderly and immunocompromised subjects, the reaction may be less than normal or even absent.
WHAT AND HOW MANY TYPES of Tuberculosis screening are there?
Lo TB screening can be done:
(1) with the tuberculin skin test
(2) with the test of interferon gamma release peptide (IGRA)
(Click here for more information)
IGRA or QUANTIFERON TEST
In addition to the Mantoux skin test, the IGRA test can be performed. This test measures the release of the protein “interferon gamma” in venous blood by lymphocytes present in a blood sample to which a specific tuberculosis antigen is added. (Click here for more information)
If you want information or to book the IGRA test, call the secretariat number +390639030481 or leave your details by clicking here.
What does the test result mean?
If the skin test or IGRA is positive, it is likely that the person has been in contact with the M. tuberculosis that infected the individual, and this infection may be latent or active. If the physician suspects an active infection, then a chest x-ray and a culture test should be performed to confirm the suspected diagnosis.
If the test result is negative, it is likely that the patient does not have TB, although this can never be definitively ruled out. The patient's lymphocytic cellular immune system may not respond to the antigen or may not have fully responded to the bacterial stimuli. In fact, approximately 6 weeks are required from the first contact with the mycobacterium for the test to provide positive results. If the screening tests provide negative results but the clinical suspicion remains, the doctor may request a new skin test or IGRA after an appropriate waiting time.
Patients infected with other mycobacterial species, such as Mycobacterium kansasii, may occasionally give false-positive results. Therefore, positive tests should always be followed by additional confirmatory tests, such as chest x-ray, to look for signs of active TB. Microbiological diagnostic tests for TB, including smears, cultures, and sensitivity tests, may also be performed to confirm the diagnosis and check the drug susceptibility of the M. tuberculosis causing the infection.
TEST RESPONSE AFTER VACCINATION
People who have been vaccinated with the BCG (bacillus Calmette-Guérin) tuberculosis vaccine generally give positive results on the skin test. The IGRA test, however, is not affected by the vaccine.
TEST ANSWERS TO PARTICULAR SITUATIONS
Additionally, a person may not respond well to the skin test (despite having had exposure to TB) if they have had a recent viral infection, have been given a live-attenuated vaccine (such as measles, mumps, chickenpox, or influenza), have another bacterial infection that suppresses TB, or are taking immunosuppressive drugs such as corticosteroids.
Typically, after receiving a vaccine with attenuated viruses, you need to wait about 4 weeks before having a skin test.
SCREENING AND PREGNANCY TESTS
It is possible to perform the screening test during pregnancy after a medical evaluation. TB can be transmitted from mother to fetus, therefore, if the mother is at risk, a skin test or IGRA may be requested. Both tests are in fact considered safe during pregnancy.
