Also known as Mantoux intradermal reaction, tuberculin sensitivity test, or PPD (Purified Protein Derivative) test, the Mantoux test is one of the main tools employed for the diagnosis of tuberculosis.
Since tuberculosis is a leading cause of death worldwide and given the recent increase in cases of the disease (in particular, caused by strains of Mycobacterium tuberculosis resistant to most antibiotics), being able to have adequate tests capable of promptly identifying the presence of the infection is fundamental. In this regard, it should be noted that the Mantoux test not only identifies current infections, but also infections On the other hand, this test also has some limitations, since there is the possibility of encountering false positive or negative results.
Several years later (around the 1930s), the American biochemist Florence Seibert was able to identify and isolate the protein portion of tuberculin directly responsible for antigenicity, thus obtaining the purified protein derivative of tuberculin (or tuberculin PPD). This discovery - in association with the method devised by Mantoux - made it possible to obtain a test considered much more reliable for the diagnosis of tuberculosis.
However, nowadays it is not uncommon for the simple name tuberculin to be used to indicate the aforementioned purified protein extract (PPD).
Therefore, currently when we talk about the Mantoux test, we are referring to the test conceived by the French doctor, but performed with the purified protein derivative tuberculin discovered in the 1930s (simply called "tuberculin"). in 0.1 ml of solution.
After a period of 48-72 hours, the patient must undergo a forearm check in order to identify and determine the reactions that occurred at the tuberculin injection site.
to determine the presence of granulomas or tubercles in the lung; or, in the event of a cough, the sputum can be analyzed, or a bronchoscopy can be performed. In any case, the doctor will have to carry out all the necessary investigations to determine if the patient has actually contracted tuberculosis.
In fact, when a positive result is obtained, it does not necessarily mean that the disease is in progress; just as when a negative result is obtained, it does not necessarily mean that the patient has not contracted the infection. In these cases, we therefore speak of false positives and false negatives.
False positives
A false positive means that the patient has tested positive for tuberculosis, but in reality the disease is not present, or not yet. In fact, the Mantoux test can be positive on several occasions:
- The patient has contracted the infection, but this is in the latent phase and, therefore, has not triggered tuberculosis. In these cases, it is customary to speak of latent tuberculosis and the implementation of the antibiotic prophylaxis protocol is envisaged. This protocol generally involves the administration of drugs such as rifampicin or isoniazid for periods of 4-7 months.
- The patient was vaccinated for tuberculosis with the BCG vaccine (containing the Calmette-Guérin bacillus).
- The patient came into contact with other non-tuberculous mycobacteria.
In light of what has just been said, in the event of a positive result in the Mantoux test - in order to make a correct diagnosis - it is very important to evaluate the individual situation of each patient (presence of any risk factors for tuberculosis, manifestation of suspicious symptoms , etc.) and, consequently, take all necessary precautions.
False negatives
Unfortunately, in the Mantoux test there is also the possibility of encountering false negative results. A classic example of a false negative is what can be obtained when the Mantoux test is performed in immunocompromised individuals. In fact, in these people, the immune system is considerably weakened and may not be able to trigger the normal defensive response against the tuberculin administered, thus giving rise to a false negative.
The Mantoux test can also give false negatives in malnourished patients and in patients receiving corticosteroid drugs or abusing steroids.
